style: fix prefer-const and prettier formatting issues

frontend/src/lib/components/account/EditRequestModal.svelte

@@ -89,57 +89,57 @@
 	);
 	let placeholderDate = $state<CalendarDate>(minDate);
 
-	let hoursUntilAppointment = $derived(
+	const hoursUntilAppointment = $derived(
 		(new SvelteDate(booking.start_time).getTime() - new SvelteDate().getTime()) / (1000 * 60 * 60)
 	);
-	let hasPayments = $derived((booking.amount_paid ?? 0) > 0);
-	let noticePeriodBlocked = $derived(
+	const hasPayments = $derived((booking.amount_paid ?? 0) > 0);
+	const noticePeriodBlocked = $derived(
 		hasPayments ? hoursUntilAppointment < 72 : hoursUntilAppointment < 24
 	);
-	let noticePeriodWarning = $derived(
+	const noticePeriodWarning = $derived(
 		!hasPayments && hoursUntilAppointment < 24 && hoursUntilAppointment >= 0
 	);
-	let noticeBlockedMessage = $derived(
+	const noticeBlockedMessage = $derived(
 		hasPayments
 			? 'This booking has payments and is too close to the original appointment to reschedule online.'
 			: 'This booking is too close to the original appointment time to reschedule online.'
 	);
 
-	let discountTotal = $derived(
+	const discountTotal = $derived(
 		booking.discounts?.reduce((sum, d) => sum + d.discount_amount, 0) ?? 0
 	);
 
-	let bookingTotalDuration = $derived(
+	const bookingTotalDuration = $derived(
 		booking.services?.reduce(
 			(sum, s) => sum + (s.override_duration_minutes ?? s.duration_minutes ?? 0),
 			0
 		) || 0
 	);
 
-	let selectedServicesDuration = $derived(
+	const selectedServicesDuration = $derived(
 		selectedServices.reduce((sum, s) => sum + (s.duration_minutes ?? 0), 0)
 	);
 
-	let hasOverrides = $derived(
+	const hasOverrides = $derived(
 		booking?.services?.some(
 			(s) => s.override_price != null || s.override_duration_minutes != null
 		) ?? false
 	);
 
-	let slotDuration = $derived(
+	const slotDuration = $derived(
 		editMode === 'time' ? bookingTotalDuration : selectedServicesDuration
 	);
 
-	let canSubmit = $derived(
+	const canSubmit = $derived(
 		submitting === false &&
 			((editMode === 'time' && !!newDate && newTime.length >= 4) ||
 				(editMode === 'services' && selectedServices.length > 0) ||
 				(editMode === 'both-time' && !!newDate && newTime.length >= 4))
 	);
 
-	let notesChanged = $derived(notes.trim() !== originalNotes.trim());
+	const notesChanged = $derived(notes.trim() !== originalNotes.trim());
 
-	let modalTitle = $derived(() => {
+	const modalTitle = $derived(() => {
 		switch (editMode) {
 			case 'select':
 				return 'Edit/Reschedule';
@@ -193,7 +193,7 @@
 
 	function calculateEndTime(startTime: string, durationMinutes: number): string {
 		const [hours, minutes] = startTime.split(':').map(Number);
-		let total = hours * 60 + minutes + durationMinutes;
+		const total = hours * 60 + minutes + durationMinutes;
 		const h = Math.floor(total / 60);
 		const m = total % 60;
 		return `${String(h).padStart(2, '0')}:${String(m).padStart(2, '0')}`;
@@ -201,7 +201,7 @@
 
 	function calculatePreviousTime(time: string): string {
 		const [h, m] = time.split(':').map(Number);
-		let total = h * 60 + m - 15;
+		const total = h * 60 + m - 15;
 		return `${String(Math.floor(total / 60)).padStart(2, '0')}:${String(total % 60).padStart(2, '0')}`;
 	}
 
@@ -654,7 +654,7 @@
 		return Math.max(0, Math.min(nextBookingStart, workingEndMinutes) - bookingEndMinutes);
 	}
 
-	let availableAdditionalServices = $derived(() => {
+	const availableAdditionalServices = $derived(() => {
 		if (editMode !== 'services') return [];
 		const remaining = calculateRemainingTime();
 		if (remaining <= 0) return [];

frontend/src/lib/components/account/UserBookingModal.svelte

@@ -21,7 +21,7 @@
 	let { open = $bindable(), bookingId }: Props = $props();
 
 	let selectedBooking = $state<Booking | null>(null);
-	let businessSettings = $derived(getBusinessInfo());
+	const businessSettings = $derived(getBusinessInfo());
 	let loading = $state(false);
 	let hasPendingEditRequest = $state(false);
 	let pendingEditRequest = $state<{
@@ -44,80 +44,80 @@
 
 	// IMPORTANT: Use override_duration_minutes when present — services may have been
 	// customised at booking time. Showing base values misleads users about what was booked.
-	let totalDuration = $derived(
+	const totalDuration = $derived(
 		selectedBooking?.services?.reduce(
 			(sum, service) => sum + (service.override_duration_minutes ?? service.duration_minutes ?? 0),
 			0
 		) || 0
 	);
 
-	let isFutureBooking = $derived(
+	const isFutureBooking = $derived(
 		selectedBooking ? new SvelteDate(selectedBooking.start_time) > new SvelteDate() : false
 	);
 
-	let hasPayments = $derived(
+	const hasPayments = $derived(
 		selectedBooking && selectedBooking.payments && selectedBooking.payments.length > 0
 	);
 
-	let isCancellable = $derived(
+	const isCancellable = $derived(
 		selectedBooking && isFutureBooking && ['pending', 'confirmed'].includes(selectedBooking.status)
 	);
 
-	let canEditBooking = $derived(isCancellable);
+	const canEditBooking = $derived(isCancellable);
 
-	let totalPaid = $derived(
+	const totalPaid = $derived(
 		selectedBooking?.payments
 			?.filter((p) => p.status === 'completed')
 			.reduce((sum, p) => sum + p.amount, 0) || 0
 	);
 
-	let totalRefunds = $derived(
+	const totalRefunds = $derived(
 		(selectedBooking?.refunds ?? [])
 			.filter((r) => r.status === 'completed')
 			.reduce((sum, r) => sum + r.amount, 0)
 	);
 
-	let balanceDue = $derived(selectedBooking ? computeBalanceDue(selectedBooking) : 0);
+	const balanceDue = $derived(selectedBooking ? computeBalanceDue(selectedBooking) : 0);
 
-	let totalVAT = $derived(
+	const totalVAT = $derived(
 		selectedBooking?.payments
 			?.filter((p) => p.status === 'completed' && p.vat_amount)
 			.reduce((sum, p) => sum + (p.vat_amount ?? 0), 0) || 0
 	);
 
-	let totalNet = $derived(
+	const totalNet = $derived(
 		selectedBooking?.payments
 			?.filter((p) => p.status === 'completed' && p.net_amount)
 			.reduce((sum, p) => sum + (p.net_amount ?? 0), 0) || 0
 	);
 
-	let hasVAT = $derived(totalVAT > 0);
+	const hasVAT = $derived(totalVAT > 0);
 
-	let depositOutstanding = $derived(
+	const depositOutstanding = $derived(
 		selectedBooking?.deposit_required && !selectedBooking?.deposit_paid
 	);
 
-	let canPayEarly = $derived(
+	const canPayEarly = $derived(
 		selectedBooking &&
 			!depositOutstanding &&
 			totalPaid < selectedBooking.total_amount &&
 			['confirmed', 'in_progress'].includes(selectedBooking.status)
 	);
 
-	let isCompleted = $derived(selectedBooking?.status === 'completed');
+	const isCompleted = $derived(selectedBooking?.status === 'completed');
 
-	let hoursUntilAppointment = $derived(
+	const hoursUntilAppointment = $derived(
 		selectedBooking
 			? (new SvelteDate(selectedBooking.start_time).getTime() - new SvelteDate().getTime()) /
 					(1000 * 60 * 60)
 			: Infinity
 	);
-	let protectedDeposit = $derived(
+	const protectedDeposit = $derived(
 		selectedBooking
 			? Math.min(totalPaid, selectedBooking.total_amount * POLICY.PROTECTED_DEPOSIT_MAX_PCT)
 			: 0
 	);
-	let estimatedRefund = $derived(
+	const estimatedRefund = $derived(
 		hoursUntilAppointment > POLICY.FULL_REFUND_THRESHOLD_HOURS
 			? totalPaid
 			: hoursUntilAppointment >= POLICY.PARTIAL_REFUND_THRESHOLD_HOURS
@@ -133,11 +133,11 @@
 	let customTipInput = $state('');
 	let tipProcessing = $state(false);
 
-	let canSaveCards = $derived(
+	const canSaveCards = $derived(
 		authStore.currentUser?.role === 'verified_email' || authStore.currentUser?.role === 'affiliate'
 	);
 
-	let tipPresets = $derived(
+	const tipPresets = $derived(
 		selectedBooking
 			? [
 					{ pct: 10, amount: Math.round(selectedBooking.total_amount * 0.1 * 100) / 100 },

frontend/src/lib/components/admin/BookingCreateModal.svelte

@@ -138,7 +138,7 @@
 			minimum_age_required: validateCsMinimumAge(newCustomService.minimum_age_required)
 		};
 	}
-	let isCustomFormValid = $derived(
+	const isCustomFormValid = $derived(
 		(newCustomService.name ?? '').trim() !== '' &&
 			!customServiceErrors.name &&
 			!customServiceErrors.price &&

frontend/src/lib/components/admin/BookingModal.svelte

@@ -32,29 +32,29 @@
 	let cancelling = $state(false);
 
 	// Derived values for cancel confirmation
-	let totalPaid = $derived(
+	const totalPaid = $derived(
 		(selectedBooking?.payments ?? [])
 			.filter((p) => p.payment_method !== 'discount' && p.status === 'completed')
 			.reduce((sum, p) => sum + p.amount, 0)
 	);
-	let totalRefunds = $derived(
+	const totalRefunds = $derived(
 		(selectedBooking?.refunds ?? [])
 			.filter((r) => r.status === 'completed')
 			.reduce((sum, r) => sum + r.amount, 0)
 	);
-	let balanceDue = $derived(selectedBooking ? computeBalanceDue(selectedBooking) : 0);
-	let hoursUntilAppt = $derived(
+	const balanceDue = $derived(selectedBooking ? computeBalanceDue(selectedBooking) : 0);
+	const hoursUntilAppt = $derived(
 		selectedBooking
 			? (new SvelteDate(selectedBooking.start_time).getTime() - new SvelteDate().getTime()) /
 					(1000 * 60 * 60)
 			: Infinity
 	);
-	let protectedDeposit = $derived(
+	const protectedDeposit = $derived(
 		selectedBooking
 			? Math.min(totalPaid, selectedBooking.total_amount * POLICY.PROTECTED_DEPOSIT_MAX_PCT)
 			: 0
 	);
-	let estimatedRefund = $derived(
+	const estimatedRefund = $derived(
 		forgiveFeesCancel
 			? totalPaid
 			: hoursUntilAppt > POLICY.FULL_REFUND_THRESHOLD_HOURS
@@ -97,7 +97,7 @@
 	// IMPORTANT: Use override_duration_minutes when present — services may have been
 	// customised at booking time (discounts, extended sessions). Showing base values
 	// misleads admins about what was actually booked.
-	let totalDuration = $derived(
+	const totalDuration = $derived(
 		selectedBooking?.services?.reduce(
 			(sum, service) => sum + (service.override_duration_minutes ?? service.duration_minutes ?? 0),
 			0

frontend/src/lib/components/admin/BookingsCard.svelte

@@ -12,7 +12,7 @@
 	import { formatUserName } from '$lib/utils/nameDisplay';
 
 	// Props
-	let { openBookingModal }: { openBookingModal: (bookingId: string) => void } = $props();
+	const { openBookingModal }: { openBookingModal: (bookingId: string) => void } = $props();
 
 	// State
 	let bookings = $state<Booking[]>([]);

frontend/src/lib/components/admin/CustomServicesManagement.svelte

@@ -25,7 +25,7 @@
 	let services = $state<CustomService[]>([]);
 	let total = $state(0);
 	let page = $state(1);
-	let perPage = $state(10);
+	const perPage = $state(10);
 	let searchQuery = $state('');
 	let loading = $state(true);
 	let creating = $state(false);
@@ -95,7 +95,7 @@
 			serviceErrors.minimum_age_required = validateMinimumAge(newService.minimum_age_required);
 	}
 
-	let isFormValid = $derived(
+	const isFormValid = $derived(
 		(newService.name ?? '').trim() !== '' &&
 			!serviceErrors.name &&
 			!serviceErrors.price &&

frontend/src/lib/components/admin/DiscountsManagement.svelte

@@ -92,7 +92,7 @@
 		}
 	});
 
-	let isFormValid = $derived.by(() => {
+	const isFormValid = $derived.by(() => {
 		if (!form.name.trim()) return false;
 		if (form.discount_percent <= 0 || form.discount_percent > 100) return false;
 		if (form.campaign_type === 'time_based') {

frontend/src/lib/components/admin/EditBookingModal.svelte

@@ -149,11 +149,11 @@
 		}
 	}
 
-	let totalDuration = $derived(
+	const totalDuration = $derived(
 		services.reduce((sum, s) => sum + (s.override_duration_minutes ?? s.duration_minutes ?? 0), 0)
 	);
 
-	let totalPrice = $derived(
+	const totalPrice = $derived(
 		services.reduce((sum, s) => sum + (s.override_price ?? s.price ?? 0), 0)
 	);
 
@@ -280,7 +280,7 @@
 		return services.some((s) => s.service_id === serviceId);
 	}
 
-	let maxAvailableDuration = $derived.by(() => {
+	const maxAvailableDuration = $derived.by(() => {
 		if (!booking?.start_time || !nextAppointmentStart) return null;
 
 		const bookingStart = new SvelteDate(booking.start_time).getTime();
@@ -292,7 +292,7 @@
 		return Math.max(0, Math.floor(availableMs / (60 * 1000)));
 	});
 
-	let filteredServices = $derived.by(() => {
+	const filteredServices = $derived.by(() => {
 		return availableServices.filter((s) => {
 			if (isServiceAdded(s.id)) return false;
 			if (maxAvailableDuration !== null && s.duration_minutes > maxAvailableDuration) return false;

frontend/src/lib/components/admin/EditRequestModal.svelte

@@ -101,7 +101,7 @@
 		return false;
 	}
 
-	let serviceDiff = $derived.by(() => {
+	const serviceDiff = $derived.by(() => {
 		const orig = editRequest.original.services;
 		const prop = editRequest.proposed.services;
 		const origIds = new Set(orig.map((s) => s.id));

frontend/src/lib/components/admin/GiftCardsManagement.svelte

@@ -37,7 +37,7 @@
 		user_balances: UserBalance[];
 	}
 
-	let summary = $state<GiftCardSummary>({
+	const summary = $state<GiftCardSummary>({
 		total_unclaimed: 0,
 		total_user_balances: 0,
 		gift_cards: [],
@@ -196,32 +196,32 @@
 	let topUpMode = $state<'giveaway' | 'purchase'>('giveaway');
 
 	// Validation
-	let generateError = $derived(
+	const generateError = $derived(
 		generateAmount && (isNaN(Number(generateAmount)) || Number(generateAmount) <= 0)
 			? 'Must be a valid positive number'
 			: ''
 	);
-	let topUpError = $derived(
+	const topUpError = $derived(
 		topUpAmount && (isNaN(Number(topUpAmount)) || Number(topUpAmount) <= 0)
 			? 'Must be a valid positive number'
 			: ''
 	);
-	let transferAmountError = $derived(
+	const transferAmountError = $derived(
 		transferAmount && (isNaN(Number(transferAmount)) || Number(transferAmount) <= 0)
 			? 'Must be a valid positive number'
 			: ''
 	);
-	let transferCodeError = $derived(
+	const transferCodeError = $derived(
 		transferToCode && transferToCode.replace(/[^a-zA-Z0-9]/g, '').length !== 12
 			? 'Code must be exactly 12 characters'
 			: ''
 	);
 
-	let isAmountValid = $derived(
+	const isAmountValid = $derived(
 		generateType === 'stock' ? true : !!(generateAmount && !generateError)
 	);
 
-	let isEmailValid = $derived.by(() => {
+	const isEmailValid = $derived.by(() => {
 		if (generateType !== 'code') return true;
 		const trimmed = generateEmail.trim();
 		if (isGuestSelected) {
@@ -233,20 +233,20 @@
 		return trimmed.includes('@') && trimmed.includes('.');
 	});
 
-	let isGenerateValid = $derived(generateType === 'stock' ? true : isAmountValid && isEmailValid);
+	const isGenerateValid = $derived(generateType === 'stock' ? true : isAmountValid && isEmailValid);
 
-	let isTopUpValid = $derived(topUpAmount && !topUpError);
-	let isTransferValid = $derived(
+	const isTopUpValid = $derived(topUpAmount && !topUpError);
+	const isTransferValid = $derived(
 		transferAmount && !transferAmountError && transferToCode && !transferCodeError
 	);
 
 	// TillPayment state
-	let showTillPayment = $state(false);
-	let tillAmount = $state(0);
-	let tillAction = $state<'create' | 'topup'>('create');
-	let tillGiftCardId = $state<string | undefined>(undefined);
-	let tillUserId = $state<string | undefined>(undefined);
-	let tillDelivery = $state<'account' | 'code'>('code');
+	const showTillPayment = $state(false);
+	const tillAmount = $state(0);
+	const tillAction = $state<'create' | 'topup'>('create');
+	const tillGiftCardId = $state<string | undefined>(undefined);
+	const tillUserId = $state<string | undefined>(undefined);
+	const tillDelivery = $state<'account' | 'code'>('code');
 
 	async function fetchGiftCards(page: number = 1, search: string = '') {
 		loading = true;
@@ -512,7 +512,7 @@
 
 	// =============== Embedded Payment Handlers ===============
 
-	let isEphemeralCardValid = $derived(
+	const isEphemeralCardValid = $derived(
 		ephemeralCardNumber.replace(/\s/g, '').length >= 13 &&
 			ephemeralCardExpiry.includes('/') &&
 			ephemeralCardExpiry.length === 5 &&
@@ -811,8 +811,11 @@
 		| 'balance'
 		| 'updated';
 
-	let cardSort = $state<{ key: SortKey; dir: 'asc' | 'desc' }>({ key: 'created', dir: 'desc' });
-	let balanceSort = $state<{ key: SortKey; dir: 'asc' | 'desc' }>({ key: 'updated', dir: 'desc' });
+	const cardSort = $state<{ key: SortKey; dir: 'asc' | 'desc' }>({ key: 'created', dir: 'desc' });
+	const balanceSort = $state<{ key: SortKey; dir: 'asc' | 'desc' }>({
+		key: 'updated',
+		dir: 'desc'
+	});
 
 	function toggleCardSort(key: SortKey) {
 		if (cardSort.key === key) {
@@ -832,7 +835,7 @@
 		}
 	}
 
-	let sortedCards = $derived.by(() => {
+	const sortedCards = $derived.by(() => {
 		let filtered = [...cards];
 		if (activeSection === 'cards') {
 			filtered = cards.filter((gc) => !isExpired(gc.last_used_at));
@@ -864,10 +867,10 @@
 		return sorted;
 	});
 
-	let activeCardsCount = $derived(cards.filter((gc) => !isExpired(gc.last_used_at)).length);
-	let expiredCardsCount = $derived(cards.filter((gc) => isExpired(gc.last_used_at)).length);
+	const activeCardsCount = $derived(cards.filter((gc) => !isExpired(gc.last_used_at)).length);
+	const expiredCardsCount = $derived(cards.filter((gc) => isExpired(gc.last_used_at)).length);
 
-	let sortedBalances = $derived.by(() => {
+	const sortedBalances = $derived.by(() => {
 		const bals = [...balances];
 		const { key, dir } = balanceSort;
 		const mul = dir === 'asc' ? 1 : -1;

frontend/src/lib/components/admin/HolidayHours.svelte

@@ -37,7 +37,7 @@
 	let exceptionGroupsLoading = $state(true);
 	let savingHours = $state(false);
 
-	let formErrors = $state({
+	const formErrors = $state({
 		name: '',
 		weeks: ''
 	});
@@ -59,7 +59,7 @@
 		]
 	});
 
-	let isFormValid = $derived(
+	const isFormValid = $derived(
 		exceptionDraft.name.trim() !== '' && exceptionDraft.weekStarts.length > 0
 	);
 

frontend/src/lib/components/admin/ImageUpload.svelte

@@ -26,7 +26,7 @@
 		return file.size > MAX_FILE_SIZE;
 	}
 
-	let hasOversizedFiles = $derived(uploadFiles.some(isFileTooBig));
+	const hasOversizedFiles = $derived(uploadFiles.some(isFileTooBig));
 
 	function isHeicFile(file: File): boolean {
 		const name = file.name.toLowerCase();

frontend/src/lib/components/admin/PatchTestsManagement.svelte

@@ -83,7 +83,7 @@
 		validateExpiryField();
 	}
 
-	let isFormValid = $derived(
+	const isFormValid = $derived(
 		formData.name.trim() !== '' &&
 			!formErrors.name &&
 			!formErrors.notice_duration &&

frontend/src/lib/components/admin/RescheduleModal.svelte

@@ -65,20 +65,20 @@
 		maxDate.getDate()
 	);
 
-	let hoursUntilAppointment = $derived(
+	const hoursUntilAppointment = $derived(
 		(new SvelteDate(booking.start_time).getTime() - new SvelteDate().getTime()) / (1000 * 60 * 60)
 	);
-	let hasPayments = $derived((booking.amount_paid ?? 0) > 0);
-	let showNoticeWarning = $derived(
+	const hasPayments = $derived((booking.amount_paid ?? 0) > 0);
+	const showNoticeWarning = $derived(
 		hasPayments ? hoursUntilAppointment < 72 : hoursUntilAppointment < 24
 	);
-	let showNoShowWarning = $derived(
+	const showNoShowWarning = $derived(
 		!hasPayments && hoursUntilAppointment < 24 && hoursUntilAppointment >= 0
 	);
 	let forgiveFees = $state(false);
 	let forgiveNoShow = $state(false);
 
-	let bookingDuration = $derived(
+	const bookingDuration = $derived(
 		booking.services?.reduce(
 			(sum, s) => sum + (s.override_duration_minutes ?? s.duration_minutes ?? 0),
 			0

frontend/src/lib/components/admin/ServicesManagement.svelte

@@ -36,9 +36,9 @@
 		is_active: true,
 		minimum_age_required: 0
 	});
-	let editingService = $state<Service | null>(null);
+	const editingService = $state<Service | null>(null);
 	let servicesLoading = $state(true);
-	let servicesUpdating = $state<Record<string, boolean>>({});
+	const servicesUpdating = $state<Record<string, boolean>>({});
 	let showServiceModal = $state(false);
 	let creatingService = $state(false);
 	let serviceErrors = $state<Record<string, string>>({});
@@ -129,7 +129,7 @@
 		);
 	}
 
-	let isFormValid = $derived(
+	const isFormValid = $derived(
 		newService.name !== '' &&
 			!serviceErrors.name &&
 			!serviceErrors.price &&

frontend/src/lib/components/admin/TillPurchases.svelte

@@ -15,8 +15,8 @@
 	let giftCardAmount = $state('25');
 	let showGiftCardInput = $state(false);
 
-	let subtotal = $derived(cart.reduce((sum, item) => sum + item.price * item.qty, 0));
-	let itemCount = $derived(cart.reduce((sum, item) => sum + item.qty, 0));
+	const subtotal = $derived(cart.reduce((sum, item) => sum + item.price * item.qty, 0));
+	const itemCount = $derived(cart.reduce((sum, item) => sum + item.qty, 0));
 
 	function formatCurrency(n: number): string {
 		return new Intl.NumberFormat('en-GB', { style: 'currency', currency: 'GBP' }).format(n);

frontend/src/lib/components/admin/TimeBlockers.svelte

@@ -55,7 +55,7 @@
 		rescheduleVersion?: number;
 	}
 
-	let { openUserModal, openBookingModal, rescheduleVersion = 0 }: Props = $props();
+	const { openUserModal, openBookingModal, rescheduleVersion = 0 }: Props = $props();
 
 	const PAGE_SIZE = 5;
 
@@ -84,7 +84,7 @@
 
 	let overlappingBookings = $state<OverlappingBooking[]>([]);
 	let hasOverlap = $state(false);
-	let hasDayConflicts = $derived(overlappingBookings.length > 0);
+	const hasDayConflicts = $derived(overlappingBookings.length > 0);
 
 	let showDeleteAlert = $state(false);
 	let blockerToDelete = $state<TimeBlocker | null>(null);
@@ -128,9 +128,9 @@
 		return `${row.startTime}-${row.endTime}-${row.isOpen}`;
 	}
 
-	let selectedWorkingHours = $derived.by(() => getWorkingHoursForDate(newStartDate));
+	const selectedWorkingHours = $derived.by(() => getWorkingHoursForDate(newStartDate));
 
-	let availableStartOptions = $derived.by(() => {
+	const availableStartOptions = $derived.by(() => {
 		const wh = selectedWorkingHours;
 		if (!wh || !wh.isOpen) return [];
 		const startMin = timeToMinutes(wh.startTime);
@@ -154,7 +154,7 @@
 		return options;
 	});
 
-	let availableEndOptions = $derived.by(() => {
+	const availableEndOptions = $derived.by(() => {
 		const wh = selectedWorkingHours;
 		if (!wh || !wh.isOpen) return [];
 		const startMin = timeToMinutes(wh.startTime);
@@ -197,14 +197,14 @@
 		return `in ${Math.floor(hr / 24)}d`;
 	}
 
-	let sortedBlockers = $derived.by(() => {
+	const sortedBlockers = $derived.by(() => {
 		return [...blockers].sort(
 			(a, b) => new SvelteDate(a.start_time).getTime() - new SvelteDate(b.start_time).getTime()
 		);
 	});
 
-	let totalPages = $derived.by(() => Math.max(1, Math.ceil(sortedBlockers.length / PAGE_SIZE)));
-	let pagedBlockers = $derived.by(() => {
+	const totalPages = $derived.by(() => Math.max(1, Math.ceil(sortedBlockers.length / PAGE_SIZE)));
+	const pagedBlockers = $derived.by(() => {
 		const start = (currentPage - 1) * PAGE_SIZE;
 		return sortedBlockers.slice(start, start + PAGE_SIZE);
 	});
@@ -275,13 +275,13 @@
 		return formatLocalDateTime(dt);
 	}
 
-	let formComplete = $derived.by(() => {
+	const formComplete = $derived.by(() => {
 		return (
 			newDescription.trim() !== '' && newStartDate !== '' && startHour !== '' && endHour !== ''
 		);
 	});
 
-	let canCreate = $derived.by(() => {
+	const canCreate = $derived.by(() => {
 		return formComplete && !hasOverlap && !hasDayConflicts && !checkingOverlap;
 	});
 

frontend/src/lib/components/admin/UsersCard.svelte

@@ -11,7 +11,7 @@
 		openUserModal: (userId: string) => void;
 	}
 
-	let { openUserModal }: Props = $props();
+	const { openUserModal }: Props = $props();
 
 	type UserListItem = {
 		id: string;

frontend/src/lib/components/admin/WalkInBooking.svelte

@@ -322,13 +322,13 @@
 		window.__walkInCountdownInterval = setInterval(updateCountdown, 1000);
 	}
 
-	let availableMinutes = $derived.by(() => {
+	const availableMinutes = $derived.by(() => {
 		if (!slotInfo) return null;
 		if (slotInfo.isAvailableNow) return getLiveRemainingMinutes();
 		return slotInfo.durationMinutes;
 	});
 
-	let tooShortForService = $derived.by(() => {
+	const tooShortForService = $derived.by(() => {
 		if (shortestServiceMinutes === null || availableMinutes === null) return false;
 		return availableMinutes < shortestServiceMinutes;
 	});

frontend/src/lib/components/admin/WalkInCreateModal.svelte

@@ -124,7 +124,7 @@
 			minimum_age_required: validateCsMinimumAge(newCustomService.minimum_age_required)
 		};
 	}
-	let isCustomFormValid = $derived(
+	const isCustomFormValid = $derived(
 		(newCustomService.name ?? '').trim() !== '' &&
 			!customServiceErrors.name &&
 			!customServiceErrors.price &&

frontend/src/lib/components/booking/BookingFlow.svelte

@@ -72,7 +72,7 @@
 	let selectedServices = $state<Service[]>([]);
 	let selectedDate = $state<CalendarDate | undefined>(undefined);
 	let selectedTime = $state<string | null>(null);
-	let customerInfo = $state<CustomerInfo>({
+	const customerInfo = $state<CustomerInfo>({
 		firstName: '',
 		lastName: '',
 		email: '',
@@ -98,13 +98,13 @@
 	let newCardNumber = $state('');
 	let newCardExpiry = $state('');
 	let newCardCVC = $state('');
-	let saveCardForFuture = $state(false);
+	const saveCardForFuture = $state(false);
 
 	// Payment flow state
 	let depositPaid = $state(false);
 	let showPaymentForm = $state(false);
 
-	let depositCardFormValid = $derived(
+	const depositCardFormValid = $derived(
 		selectedPaymentMethod !== null ||
 			(showNewCardForm &&
 				newCardNumber.replace(/\s/g, '').length >= 13 &&
@@ -113,17 +113,17 @@
 	);
 
 	// VAT registration status from public business info (via shared store)
-	let vatRegistered = $derived(getBusinessInfo()?.is_vat_registered ?? false);
+	const vatRegistered = $derived(getBusinessInfo()?.is_vat_registered ?? false);
 
 	// Email existence check (guest flow only)
 	let emailChecking = $state(false);
 	let emailSuggestion = $state<string | null>(null);
 	let emailError = $state('');
-	let emailFormatValid = $derived(
+	const emailFormatValid = $derived(
 		!customerInfo.email ||
 			/^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/.test(customerInfo.email)
 	);
-	let allGuestFieldsValid = $derived(
+	const allGuestFieldsValid = $derived(
 		customerInfo.firstName &&
 			customerInfo.lastName &&
 			customerInfo.email &&
@@ -571,12 +571,12 @@
 	let loadingWorkingHours = $state<boolean>(false);
 	let loadingAvailableHours = $state<boolean>(false);
 
-	let workingHoursCache: Record<
+	const workingHoursCache: Record<
 		string,
 		Record<string, { isOpen: boolean; startTime: string; endTime: string }>
 	> = {};
 
-	let availableHoursCache: Record<
+	const availableHoursCache: Record<
 		string,
 		Record<string, { isOpen: boolean; slots: Array<{ startTime: string; endTime: string }> }>
 	> = {};
@@ -602,7 +602,7 @@
 	});
 
 	// Track which months are currently being fetched (prevents duplicate requests)
-	let loadingMonths: Record<string, boolean> = {};
+	const loadingMonths: Record<string, boolean> = {};
 
 	// Preload current + next month on first render; subsequent months fetched individually
 	let initialLoadDone = $state(false);
@@ -1304,13 +1304,13 @@
 		selectedDate ? getDayWithOrdinal(selectedDate) : undefined
 	);
 
-	let depositRequired = $derived(calculateDepositRequired());
-	let totalSteps = $derived(authStore.isAuthenticated ? 4 : 5);
+	const depositRequired = $derived(calculateDepositRequired());
+	const totalSteps = $derived(authStore.isAuthenticated ? 4 : 5);
 	// StepIndicator uses displayNumber = startAt + index. currentStep aligns with displayNumber,
 	// not the array index. For auth: startAt=1, totalSteps=4 → last displayNumber=4.
 	// For guest: startAt=0, totalSteps=5 → last displayNumber=4. Always evaluates to 4.
-	let finalStep = $derived(totalSteps - 1 + (authStore.isAuthenticated ? 1 : 0));
-	let stepLabels = $derived(
+	const finalStep = $derived(totalSteps - 1 + (authStore.isAuthenticated ? 1 : 0));
+	const stepLabels = $derived(
 		authStore.isAuthenticated
 			? ['Service', 'Date & Time', 'Details', 'Payment']
 			: userDepositsRequired > 0

frontend/src/lib/components/booking/BookingSummary.svelte

@@ -4,7 +4,7 @@
 	import { getLocalTimeZone } from '@internationalized/date';
 	import { Separator } from '$lib/components/ui/separator';
 
-	let {
+	const {
 		services = [],
 		date = undefined,
 		time = null,

frontend/src/lib/components/booking/DatePicker.svelte

@@ -2,7 +2,7 @@
 	import type { CalendarDate, DateValue } from '@internationalized/date';
 	import Calendar from '$lib/components/ui/calendar/calendar.svelte';
 
-	let {
+	const {
 		date,
 		placeholder,
 		minValue,

frontend/src/lib/components/booking/SelectedTimeSummary.svelte

@@ -11,7 +11,7 @@
 		outOfHours?: boolean;
 	}
 
-	let {
+	const {
 		selectedDate,
 		selectedTime,
 		endTime,

frontend/src/lib/components/booking/ServiceCard.svelte

@@ -2,7 +2,7 @@
 	import { resolve } from '$app/paths';
 	import type { Service } from '$lib/types/booking';
 
-	let {
+	const {
 		service,
 		selected = false,
 		onclick,

frontend/src/lib/components/booking/ServiceSelector.svelte

@@ -2,7 +2,7 @@
 	import ServiceCard from './ServiceCard.svelte';
 	import type { Service } from '$lib/types/booking';
 
-	let {
+	const {
 		services = [],
 		selected = [],
 		loading = true,

frontend/src/lib/components/booking/TimeSlotList.svelte

@@ -11,7 +11,7 @@
 		onSelect: (time: string) => void;
 	}
 
-	let { slots, selectedTime, duration, protection, onSelect }: Props = $props();
+	const { slots, selectedTime, duration, protection, onSelect }: Props = $props();
 </script>
 
 {#if slots.length > 0}

frontend/src/lib/components/booking/TimeSlotPicker.svelte

@@ -2,7 +2,7 @@
 	import type { CalendarDate } from '@internationalized/date';
 	import { Button } from '$lib/components/ui/button';
 
-	let {
+	const {
 		date,
 		groupedTimeSlots = [],
 		selectedTime = null,

frontend/src/lib/components/layout/NavBar.svelte

@@ -52,8 +52,8 @@
 	};
 
 	// Derived values for auth state - ensures reactivity
-	let isAuthenticated = $derived(authStore.isAuthenticated);
-	let isLoading = $derived(authStore.isLoading);
+	const isAuthenticated = $derived(authStore.isAuthenticated);
+	const isLoading = $derived(authStore.isLoading);
 
 	// Notification bell state
 	let unreadCount = $state(0);

frontend/src/lib/components/payments/PaymentModal.svelte

@@ -15,7 +15,7 @@
 		onComplete: (payment: PaymentResult) => void;
 	}
 
-	let { booking, onClose, onComplete }: Props = $props();
+	const { booking, onClose, onComplete }: Props = $props();
 
 	type PaymentStatus =
 		| 'idle'
@@ -47,17 +47,17 @@
 	let paymentResult = $state<PaymentResult | null>(null);
 	let error = $state<string | null>(null);
 
-	let stamps = $derived(booking.user?.loyalty_stamps ?? 0);
+	const stamps = $derived(booking.user?.loyalty_stamps ?? 0);
 	let useLoyalty = $state(false);
 
-	let loyaltyEligible = $derived(
+	const loyaltyEligible = $derived(
 		stamps >= 10 &&
 			!(booking.discounts ?? []).some((d: BookingDiscount) => d.discount_source === 'loyalty') &&
 			booking.total_amount > 0 &&
 			booking.amount_paid === 0
 	);
 
-	let loyaltyDiscount = $derived(
+	const loyaltyDiscount = $derived(
 		useLoyalty ? Math.round(booking.total_amount * 100 * LOYALTY_DISCOUNT_RATE) : 0
 	);
 
@@ -203,13 +203,15 @@
 		return service.override_price ?? service.price ?? 0;
 	}
 
-	let subtotal = $derived((booking.services ?? []).reduce((sum, s) => sum + getServicePrice(s), 0));
-	let discountSum = $derived(
+	const subtotal = $derived(
+		(booking.services ?? []).reduce((sum, s) => sum + getServicePrice(s), 0)
+	);
+	const discountSum = $derived(
 		(booking.discounts ?? []).reduce((sum, d) => sum + d.discount_amount, 0)
 	);
-	let netTotal = $derived(Math.max(0, subtotal - discountSum));
+	const netTotal = $derived(Math.max(0, subtotal - discountSum));
 
-	let tipPercentages = $derived.by(() => {
+	const tipPercentages = $derived.by(() => {
 		if (netTotal <= 0) return [];
 		return [
 			{ pct: 10, amount: Math.round(netTotal * 0.1 * 100) / 100 },
@@ -218,7 +220,7 @@
 		];
 	});
 
-	let tipMultiplier = $derived(
+	const tipMultiplier = $derived(
 		selectedTipPercent !== null
 			? 1 + selectedTipPercent / 100
 			: customTipAmount && parseFloat(customTipAmount) > 0
@@ -226,8 +228,8 @@
 				: 1
 	);
 
-	let totalWithTip = $derived(tipEnabled ? netTotal * tipMultiplier : netTotal);
-	let tipDisplay = $derived(
+	const totalWithTip = $derived(tipEnabled ? netTotal * tipMultiplier : netTotal);
+	const tipDisplay = $derived(
 		selectedTipPercent !== null
 			? `${selectedTipPercent}%`
 			: customTipAmount && parseFloat(customTipAmount) > 0
@@ -235,7 +237,7 @@
 				: ''
 	);
 
-	let totalDue = $derived(tipEnabled ? totalWithTip : netTotal);
+	const totalDue = $derived(tipEnabled ? totalWithTip : netTotal);
 
 	function formatCurrency(value: number): string {
 		return new Intl.NumberFormat('en-GB', {
@@ -378,8 +380,8 @@
 	});
 
 	let cashAmount = $state<string>('');
-	let cashAmountNum = $derived(cashAmount === '' ? 0 : parseFloat(cashAmount));
-	let changeDue = $derived(cashAmountNum > totalDue ? cashAmountNum - totalDue : 0);
+	const cashAmountNum = $derived(cashAmount === '' ? 0 : parseFloat(cashAmount));
+	const changeDue = $derived(cashAmountNum > totalDue ? cashAmountNum - totalDue : 0);
 	let extraAsTip = $state(false);
 
 	function handleCashInput(e: Event) {
@@ -511,7 +513,7 @@
 		giftCardId = formatted;
 	}
 
-	let giftCardValid = $derived(useAccountBalance || giftCardId.replace(/-/g, '').length === 12);
+	const giftCardValid = $derived(useAccountBalance || giftCardId.replace(/-/g, '').length === 12);
 
 	async function handleGiftCardPayment() {
 		if (!giftCardValid) {

frontend/src/lib/components/payments/TillPaymentModal.svelte

@@ -21,7 +21,7 @@
 		onComplete: (result: TillSaleResult) => void;
 	}
 
-	let {
+	const {
 		amount,
 		itemType,
 		action,
@@ -100,9 +100,9 @@
 
 	// Cash
 	let cashAmount = $state('');
-	let cashAmountNum = $derived(Number(cashAmount) || 0);
-	let changeDue = $derived(Math.max(0, cashAmountNum - amount));
-	let cashEntryComplete = $derived(cashAmountNum >= amount);
+	const cashAmountNum = $derived(Number(cashAmount) || 0);
+	const changeDue = $derived(Math.max(0, cashAmountNum - amount));
+	const cashEntryComplete = $derived(cashAmountNum >= amount);
 	// Remember cash received for success screen display
 	let cashTendered = $state(0);
 
@@ -224,13 +224,13 @@
 		ephemeralCardCVC = input.value.replace(/\D/g, '').substring(0, 4);
 	}
 
-	let isEphemeralCardValid = $derived(
+	const isEphemeralCardValid = $derived(
 		isValidLuhn(ephemeralCardNumber) &&
 			/^\d{2}\/\d{2}$/.test(ephemeralCardExpiry) &&
 			ephemeralCardCVC.length >= 3
 	);
 
-	let ephemeralCardError = $derived(
+	const ephemeralCardError = $derived(
 		ephemeralCardNumber.length > 0 && !isValidLuhn(ephemeralCardNumber)
 			? 'Invalid card number'
 			: /^\d{2}\/\d{2}$/.test(ephemeralCardExpiry) &&

frontend/src/lib/components/payments/UserPaymentModal.svelte

@@ -22,7 +22,7 @@
 		defaultPaymentType?: 'full' | 'partial' | 'deposit';
 	}
 
-	let { booking, onClose, onComplete, canSaveCards = true, defaultPaymentType }: Props = $props();
+	const { booking, onClose, onComplete, canSaveCards = true, defaultPaymentType }: Props = $props();
 
 	type PaymentStatus = 'idle' | 'processing' | 'polling' | 'success' | 'error';
 
@@ -140,9 +140,9 @@
 		return { month, year };
 	}
 
-	let expiryParts = $derived(parseExpiryParts(newCardExpiry));
+	const expiryParts = $derived(parseExpiryParts(newCardExpiry));
 
-	let isExpiryInPast = $derived(
+	const isExpiryInPast = $derived(
 		expiryParts !== null &&
 			(() => {
 				const expiryDate = new SvelteDate(expiryParts.year, expiryParts.month);
@@ -150,7 +150,7 @@
 			})()
 	);
 
-	let hasInvalidMonth = $derived(/^\d{2}\/\d{2}$/.test(newCardExpiry) && expiryParts === null);
+	const hasInvalidMonth = $derived(/^\d{2}\/\d{2}$/.test(newCardExpiry) && expiryParts === null);
 
 	function isValidLuhn(cardNumber: string): boolean {
 		const s = cardNumber.replace(/\D/g, '');
@@ -168,17 +168,17 @@
 		return sum % 10 === 0 && s.length >= 13 && s.length <= 19;
 	}
 
-	let cardFormValid = $derived(
+	const cardFormValid = $derived(
 		isValidLuhn(newCardNumber) && expiryParts !== null && newCardCVC.length >= 3 && !isExpiryInPast
 	);
 
-	let cardSelected = $derived(
+	const cardSelected = $derived(
 		(selectedPaymentMethod !== null && paymentMethods.length > 0) ||
 			(showNewCardForm && cardFormValid) ||
 			(paymentMethods.length === 0 && cardFormValid)
 	);
 
-	let cardValidationError = $derived(
+	const cardValidationError = $derived(
 		!cardSelected
 			? selectedPaymentMethod === null && paymentMethods.length > 0 && !showNewCardForm
 				? 'Please select a card'
@@ -211,12 +211,12 @@
 	} | null>(null);
 
 	// Derived values
-	let depositOutstanding = $derived(booking.deposit_required && !booking.deposit_paid);
+	const depositOutstanding = $derived(booking.deposit_required && !booking.deposit_paid);
 
 	// Auto-select a sensible default payment type based on the booking's deposit
 	// state. The backend will split the charge into deposit + non-deposit records
 	// when appropriate, so this choice mainly controls the button label and amount.
-	let defaultType = $derived(defaultPaymentType ?? (depositOutstanding ? 'deposit' : 'full'));
+	const defaultType = $derived(defaultPaymentType ?? (depositOutstanding ? 'deposit' : 'full'));
 	let paymentType = $state<'full' | 'partial' | 'deposit'>('full');
 	$effect(() => {
 		paymentType = defaultType as 'full' | 'partial' | 'deposit';
@@ -230,35 +230,35 @@
 	let lockInterval: ReturnType<typeof setInterval> | null = null;
 	let countdownInterval: ReturnType<typeof setInterval> | null = null;
 
-	let servicesSubtotal = $derived(
+	const servicesSubtotal = $derived(
 		(booking.services ?? []).reduce((sum, s) => sum + (s.price || 0), 0)
 	);
-	let discountSum = $derived(
+	const discountSum = $derived(
 		(booking.discounts ?? []).reduce((sum, d) => sum + d.discount_amount, 0)
 	);
 
-	let totalPaid = $derived(
+	const totalPaid = $derived(
 		booking.payments
 			?.filter((p) => p.status === 'completed')
 			.reduce((sum, p) => sum + p.amount, 0) || 0
 	);
 
-	let amountRemaining = $derived(booking.total_amount - totalPaid);
+	const amountRemaining = $derived(booking.total_amount - totalPaid);
 
-	let loyaltyEligible = $derived(
+	const loyaltyEligible = $derived(
 		stamps >= 10 &&
 			!(booking.discounts ?? []).some((d) => d.discount_source === 'loyalty') &&
 			booking.total_amount > 0 &&
 			booking.amount_paid === 0
 	);
 
-	let loyaltyDiscount = $derived(
+	const loyaltyDiscount = $derived(
 		useLoyalty ? Math.round(booking.total_amount * 100 * LOYALTY_DISCOUNT_RATE) : 0
 	);
 
 	// Deposit policy warning text — dynamic based on booking state
-	let expectedDepositPercent = $derived(booking.deposit_required ? 20 : 0);
-	let depositPolicyWarning = $derived<string | null>(
+	const expectedDepositPercent = $derived(booking.deposit_required ? 20 : 0);
+	const depositPolicyWarning = $derived<string | null>(
 		{
 			get text(): string | null {
 				if (!booking.deposit_required && totalPaid === 0 && booking.amount_due <= 0) return null;
@@ -273,12 +273,12 @@
 		}.text
 	);
 
-	let isScenarioA = $derived(depositOutstanding);
+	const isScenarioA = $derived(depositOutstanding);
 
-	let isScenarioB = $derived(!depositOutstanding && totalPaid < booking.total_amount);
+	const isScenarioB = $derived(!depositOutstanding && totalPaid < booking.total_amount);
 
-	let partialAmountNum = $derived(partialAmount === '' ? 0 : parseFloat(partialAmount));
-	let partialAmountValid = $derived(
+	const partialAmountNum = $derived(partialAmount === '' ? 0 : parseFloat(partialAmount));
+	const partialAmountValid = $derived(
 		paymentType === 'partial' &&
 			partialAmount !== '' &&
 			!isNaN(partialAmountNum) &&
@@ -287,7 +287,7 @@
 			/^\d+(\.\d{0,2})?$/.test(partialAmount)
 	);
 
-	let partialValidationError = $derived(
+	const partialValidationError = $derived(
 		paymentType === 'partial' && !partialAmountValid
 			? partialAmount === ''
 				? 'Enter an amount'
@@ -301,14 +301,14 @@
 			: null
 	);
 
-	let payButtonDisabled = $derived(
+	const payButtonDisabled = $derived(
 		status === 'processing' ||
 			!cardSelected ||
 			(paymentType === 'partial' && !partialAmountValid) ||
 			(booking.status === 'pending_release' && (lockTimer <= 0 || !lockAcquired))
 	);
 
-	let payButtonError = $derived(
+	const payButtonError = $derived(
 		status === 'processing'
 			? null
 			: !cardSelected

frontend/src/lib/components/today/CurrentAppointment.svelte

@@ -18,7 +18,7 @@
 		openUserModal: (userId: string) => void;
 	}
 
-	let { _openBookingModal, openEditBookingModal, openUserModal }: Props = $props();
+	const { _openBookingModal, openEditBookingModal, openUserModal }: Props = $props();
 
 	type Booking = {
 		id: string;
@@ -90,7 +90,7 @@
 	let weekSummary = $state<DailySummary | null>(null);
 
 	// VAT registration status from public business info (via shared store)
-	let vatRegistered = $derived(getBusinessInfo()?.is_vat_registered ?? false);
+	const vatRegistered = $derived(getBusinessInfo()?.is_vat_registered ?? false);
 
 	// Data diffing — only update UI when payload actually changes
 	let prevDataJson = $state('');

frontend/src/lib/components/today/PendingApprovals.svelte

@@ -87,17 +87,17 @@
 	};
 
 	let pendingApprovals = $state<PendingApproval[]>([]);
-	let visibleApprovals = $derived(pendingApprovals.slice(0, 3));
+	const visibleApprovals = $derived(pendingApprovals.slice(0, 3));
 	let loading = $state(true);
 	let showApprovalModal = $state(false);
 	let selectedBooking = $state<PendingBooking | null>(null);
 
 	let pendingEditRequests = $state<EditRequest[]>([]);
-	let visibleEditRequests = $derived(pendingEditRequests.slice(0, 3));
+	const visibleEditRequests = $derived(pendingEditRequests.slice(0, 3));
 	let showEditRequestModal = $state(false);
 	let selectedEditRequest = $state<EditRequest | null>(null);
 
-	let _hasItems = $derived(pendingApprovals.length > 0 || pendingEditRequests.length > 0);
+	const _hasItems = $derived(pendingApprovals.length > 0 || pendingEditRequests.length > 0);
 	$effect(() => {
 		hasItems = _hasItems;
 	});

frontend/src/lib/components/today/TodayCalendar.svelte

@@ -28,7 +28,7 @@
 		openUserModal: (userId: string) => void;
 	}
 
-	let { openBookingModal, openUserModal }: Props = $props();
+	const { openBookingModal, openUserModal }: Props = $props();
 
 	type TodayAppointment = {
 		id: string;
@@ -155,7 +155,7 @@
 		return blocker.description?.startsWith('RESERVATION:') ?? false;
 	}
 
-	let availableStartOptions = $derived.by(() => {
+	const availableStartOptions = $derived.by(() => {
 		const wh = workingHours;
 		if (!wh || !wh.isOpen) return [];
 		const startMin = timeToMinutes(wh.startTime);
@@ -174,7 +174,7 @@
 		return options;
 	});
 
-	let availableEndOptions = $derived.by(() => {
+	const availableEndOptions = $derived.by(() => {
 		const wh = workingHours;
 		if (!wh || !wh.isOpen) return [];
 		const endMin = timeToMinutes(wh.endTime);
@@ -197,7 +197,7 @@
 		return options;
 	});
 
-	let suggestedLunch = $derived.by(() => {
+	const suggestedLunch = $derived.by(() => {
 		if (!workingHours || !availableHours || !workingHours.isOpen) return null;
 		const wh = workingHours;
 		const ah = availableHours;
@@ -284,7 +284,7 @@
 		| LunchTimelineItem
 		| ClosingTimeTimelineItem;
 
-	let timeline = $derived.by(() => {
+	const timeline = $derived.by(() => {
 		const items: TimelineItem[] = [];
 
 		for (const apt of appointments) {
@@ -512,7 +512,7 @@
 		return formatLocalDateTime(dt);
 	}
 
-	let canCreate = $derived.by(() => !hasOverlap && !checkingOverlap);
+	const canCreate = $derived.by(() => !hasOverlap && !checkingOverlap);
 
 	async function createBlocker() {
 		if (!canCreate) return;

frontend/src/lib/components/ui/CharCounter.svelte

@@ -4,7 +4,7 @@
 		maxChars?: number;
 		threshold?: number; // when to start showing counter
 	};
-	let { text, maxChars = 1000000, threshold = 750000 }: Props = $props();
+	const { text, maxChars = 1000000, threshold = 750000 }: Props = $props();
 
 	const graphemeCount = $derived.by(() => {
 		const segmenter = new Intl.Segmenter('en', { granularity: 'grapheme' });

frontend/src/lib/components/ui/ImageVariant.svelte

@@ -12,7 +12,7 @@
 		jxl?: string;
 	}
 
-	let {
+	const {
 		urls,
 		type = 'thumb',
 		alt = '',

frontend/src/lib/components/ui/StatusBadge.svelte

@@ -1,5 +1,5 @@
 <script lang="ts">
-	let { status }: { status: string } = $props();
+	const { status }: { status: string } = $props();
 
 	const variantMap: Record<string, { label: string; variantClass: string }> = {
 		draft: { label: 'Draft', variantClass: 'bg-gray-100 text-gray-800' },

frontend/src/lib/components/ui/form/form-button.svelte

@@ -1,7 +1,7 @@
 <script lang="ts">
 	import * as Button from '$lib/components/ui/button/index.js';
 
-	let { ...restProps }: Record<string, unknown> = $props();
+	const { ...restProps }: Record<string, unknown> = $props();
 	let ref = $state<HTMLElement | null>(null);
 </script>
 

frontend/src/lib/components/ui/image-cropper/image-cropper-cropper.svelte

@@ -3,7 +3,7 @@
 	import { useImageCropperCropper } from './image-cropper.svelte.js';
 	import type { ImageCropperCropperProps } from './types.js';
 
-	let {
+	const {
 		cropShape = 'round',
 		aspect = 1,
 		showGrid = false,

frontend/src/lib/components/ui/image-cropper/image-cropper-dialog.svelte

@@ -4,7 +4,7 @@
 	import { useImageCropperDialog } from './image-cropper.svelte.js';
 	import type { ImageCropperDialogProps } from './types';
 
-	let { children, class: className, ...rest }: ImageCropperDialogProps = $props();
+	const { children, class: className, ...rest }: ImageCropperDialogProps = $props();
 
 	const dialogState = useImageCropperDialog();
 </script>

frontend/src/lib/components/ui/image-cropper/image-cropper-preview.svelte

@@ -5,7 +5,7 @@
 	import UploadIcon from '@lucide/svelte/icons/upload';
 	import { cn } from '$lib/utils.js';
 
-	let { child, class: className }: ImageCropperPreviewProps = $props();
+	const { child, class: className }: ImageCropperPreviewProps = $props();
 
 	const previewState = useImageCropperPreview();
 </script>

frontend/src/lib/components/ui/map/MapArc.svelte

@@ -52,7 +52,7 @@
 <script lang="ts" generics="T extends MapArcDatum = MapArcDatum">
 	import { useMap } from '$lib/hooks/use-map.svelte.js';
 
-	let {
+	const {
 		data,
 		id: propId,
 		curvature = 0.2,
@@ -80,7 +80,7 @@
 	const ARC_HIT_MIN_WIDTH = 12;
 	const ARC_HIT_PADDING = 6;
 
-	let autoId = $state(Math.random().toString(36).slice(2));
+	const autoId = $state(Math.random().toString(36).slice(2));
 	const id = $derived(propId ?? autoId);
 	const sourceId = $derived(`arc-source-${id}`);
 	const layerId = $derived(`arc-layer-${id}`);

frontend/src/lib/components/ui/map/MapClusterLayer.svelte

@@ -25,7 +25,7 @@
 		onclusterclick?: (clusterId: number, coordinates: [number, number], pointCount: number) => void;
 	}
 
-	let {
+	const {
 		data,
 		clusterMaxZoom = 14,
 		clusterRadius = 50,

frontend/src/lib/components/ui/map/MapControls.svelte

@@ -18,7 +18,7 @@
 		onlocate?: (coords: { longitude: number; latitude: number }) => void;
 	}
 
-	let {
+	const {
 		position = 'bottom-right',
 		showZoom = true,
 		showCompass = false,

frontend/src/lib/components/ui/map/MapMarker.svelte

@@ -31,7 +31,7 @@
 		rotationAlignment?: MarkerOptions['rotationAlignment'];
 	}
 
-	let {
+	const {
 		longitude,
 		latitude,
 		children,

frontend/src/lib/components/ui/map/MapPopup.svelte

@@ -19,7 +19,7 @@
 		maxWidth?: string;
 	}
 
-	let {
+	const {
 		longitude,
 		latitude,
 		children,

frontend/src/lib/components/ui/map/MapRoute.svelte

@@ -26,7 +26,7 @@
 		interactive?: boolean;
 	}
 
-	let {
+	const {
 		coordinates,
 		color = '#4285F4',
 		width = 3,

frontend/src/lib/components/ui/map/MarkerContent.svelte

@@ -8,7 +8,7 @@
 		class?: string;
 	}
 
-	let { children, class: className }: Props = $props();
+	const { children, class: className }: Props = $props();
 
 	const markerCtx = getContext<{
 		getMarker: () => MapLibreGL.Marker | null;

frontend/src/lib/components/ui/map/MarkerLabel.svelte

@@ -7,7 +7,7 @@
 		position?: 'top' | 'bottom';
 	}
 
-	let { children, class: className, position = 'top' }: Props = $props();
+	const { children, class: className, position = 'top' }: Props = $props();
 
 	const positionClasses = {
 		top: 'bottom-full mb-1',

frontend/src/lib/components/ui/map/MarkerPopup.svelte

@@ -16,7 +16,7 @@
 		maxWidth?: string;
 	}
 
-	let {
+	const {
 		children,
 		class: className,
 		closeButton = false,

frontend/src/lib/components/ui/map/MarkerTooltip.svelte

@@ -10,7 +10,7 @@
 		anchor?: PopupOptions['anchor'];
 	}
 
-	let { children, class: className, offset = 16, anchor }: Props = $props();
+	const { children, class: className, offset = 16, anchor }: Props = $props();
 
 	const markerCtx = getContext<{
 		getMarker: () => MapLibreGL.Marker | null;

frontend/src/lib/components/ui/policyPopover.svelte

@@ -1,7 +1,7 @@
 <script lang="ts">
 	import type { Snippet } from 'svelte';
 
-	let {
+	const {
 		trigger
 	}: {
 		trigger?: Snippet;

frontend/src/lib/components/ui/sonner/sonner.svelte

@@ -2,7 +2,7 @@
 	import { Toaster as Sonner, type ToasterProps as SonnerProps } from 'svelte-sonner';
 	import { mode } from 'mode-watcher';
 
-	let { ...restProps }: SonnerProps = $props();
+	const { ...restProps }: SonnerProps = $props();
 </script>
 
 <Sonner

frontend/src/lib/utils/timeSlots.ts

@@ -120,7 +120,7 @@ export function timeToMinutes(time: string): number {
 
 export function calculatePreviousTime(time: string): string {
 	const [hours, minutes] = time.split(':').map(Number);
-	let totalMinutes = hours * 60 + minutes - 15;
+	const totalMinutes = hours * 60 + minutes - 15;
 	return `${String(Math.floor(totalMinutes / 60)).padStart(2, '0')}:${String(totalMinutes % 60).padStart(2, '0')}`;
 }
 
@@ -208,7 +208,7 @@ export function generateAvailableTimeSlots(
 			});
 			const [londonHours, londonMinutes] = londonTimeStr.split(':').map(Number);
 			const currentMinutes = londonHours * 60 + londonMinutes;
-			let minimumStart = Math.ceil((currentMinutes + 60) / 15) * 15;
+			const minimumStart = Math.ceil((currentMinutes + 60) / 15) * 15;
 			startTotalMinutes = Math.max(startTotalMinutes, minimumStart);
 		}