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/ui/dialog/dialog-content.svelte

@@ -20,7 +20,7 @@
 </script>
 
 <Dialog.Portal {...portalProps}>
-	<Dialog.Overlay />
+	<Dialog.Overlay class={typeof className === 'string' && /(!?z-\[[^\]]+\]|!?z-\d+)/.test(className) ? className.match(/(!?z-\[[^\]]+\]|!?z-\d+)/)?.[0] : ''} />
 	<DialogPrimitive.Content
 		bind:ref
 		data-slot="dialog-content"