feat(loyalty-discount): implement loyalty and discount system

- Add discount campaign management and validation logic
- Update booking handlers with discount application flow
- Add customer relationship endpoints for loyalty tracking
- Update frontend modals (booking, approval, payment, reschedule)
- Add DiscountsManagement and loyalty reference documentation
- Update dev scripts and database init for discount tables
- Clean up completed plan files

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

@@ -382,7 +382,7 @@
 </script>
 
 <Dialog.Root open={true} onOpenChange={(open) => !open && handleClose()}>
-	<Dialog.Content class="max-h-[90vh] max-w-md overflow-y-auto">
+	<Dialog.Content class="!z-[70] max-h-[90vh] max-w-md overflow-y-auto">
 		<Dialog.Header>
 			<Dialog.Title class="text-xl font-semibold">Make a Payment</Dialog.Title>
 			{#if booking.id}