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/admin/RescheduleModal.svelte

@@ -408,7 +408,7 @@
 </script>
 
 <Modal.Root bind:open>
-	<Modal.Content class="max-h-[90vh] max-w-4xl overflow-y-auto">
+	<Modal.Content class="!z-[70] max-h-[90vh] max-w-4xl overflow-y-auto">
 		<Modal.Header>
 			<Modal.Title class="text-lg font-semibold">Reschedule Booking</Modal.Title>
 			<Modal.Description>