style: fix prefer-const and prettier formatting issues

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 },