style: fix prefer-const and prettier formatting issues

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