fix: persist service price overrides before payment

Service price overrides in PaymentModal were only used for frontend
calculations but not persisted to the backend. This caused receipts
and subsequent payments to use original prices instead of overridden
ones.

Added saveServiceOverrides() function that calls PUT
/api/admin/bookings/{id}/services before payment to persist any
price changes. Called in both handleCardPayment and
handleSavedCardPayment before applyLoyaltyRedemption().

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

@@ -460,6 +460,47 @@
 		}
 	}
 
+	async function saveServiceOverrides(): Promise<void> {
+		// Check if any service has an override that differs from the original price
+		const services = booking.services ?? [];
+		const hasOverrides = services.some((s) => {
+			const override = serviceOverrides[s.service_id];
+			if (!override) return false;
+			const overridePrice = parseFloat(override.price);
+			return !isNaN(overridePrice) && Math.abs(overridePrice - override.originalPrice) > 0.01;
+		});
+
+		if (!hasOverrides) return;
+
+		// Build the request payload
+		const serviceIds = services.map((s) => s.service_id).filter((id): id is string => !!id);
+		const serviceOverridesPayload = services
+			.filter((s) => {
+				const override = serviceOverrides[s.service_id];
+				if (!override) return false;
+				const overridePrice = parseFloat(override.price);
+				return !isNaN(overridePrice) && Math.abs(overridePrice - override.originalPrice) > 0.01;
+			})
+			.map((s) => ({
+				service_id: s.service_id,
+				override_price: parseFloat(serviceOverrides[s.service_id].price)
+			}));
+
+		const res = await apiFetch(`/api/admin/bookings/${booking.id}/services`, {
+			method: 'PUT',
+			headers: { 'Content-Type': 'application/json' },
+			body: JSON.stringify({
+				service_ids: serviceIds,
+				service_overrides: serviceOverridesPayload
+			})
+		});
+
+		if (!res.ok) {
+			const errData = await res.text();
+			throw new Error(extractErrorMessage(errData) || 'Failed to save service overrides');
+		}
+	}
+
 	async function handleCardPayment() {
 		if (isProcessingPaymentSync) return;
 		const finalAmount = cardAmountNum;
@@ -484,6 +525,7 @@
 		error = null;
 
 		try {
+			await saveServiceOverrides();
 			await applyLoyaltyRedemption();
 
 			const response = await apiFetch(`/api/admin/bookings/${booking.id}/payment`, {
@@ -961,6 +1003,7 @@
 
 		let responseStatus = 0;
 		try {
+			await saveServiceOverrides();
 			await applyLoyaltyRedemption();
 
 			// Proactive saved-card (ccof) SCA: run the client-side challenge