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/UserModal.svelte

@@ -72,6 +72,7 @@
 
 	type CustomerRelationship = {
 		totalSpend: number;
+		totalSaved: number;
 		totalTips: number;
 		totalVisits: number;
 		customerFor: string;
@@ -485,13 +486,19 @@
 						<h3 class="mb-3 text-sm font-semibold tracking-wide text-gray-600 uppercase">
 							Customer Relationship
 						</h3>
-						<div class="grid gap-3 md:grid-cols-3">
+						<div class="grid gap-3 md:grid-cols-5">
 							<div>
 								<div class="text-xs text-gray-500">Total Spend</div>
 								<div class="text-2xl font-bold text-emerald-600">
 									£{customerRelationship.totalSpend.toFixed(2)}
 								</div>
 							</div>
+							<div>
+								<div class="text-xs text-gray-500">Total Saved</div>
+								<div class="text-2xl font-bold text-fuchsia-600">
+									£{customerRelationship.totalSaved.toFixed(2)}
+								</div>
+							</div>
 							<div>
 								<div class="text-xs text-gray-500">Total Tips</div>
 								<div class="text-2xl font-bold text-amber-600">