feat: Enhance booking functionality with invoice management and dashboard summary

- Added customerId to guest booking requests for better identification.
- Implemented new endpoints for managing booking invoices and dashboard summaries.
- Created BookingInvoice and BookingDashboardSummary DTOs to support new features.
- Updated Booking and BookingInvoice models to include payment method and timestamps.
- Enhanced BookingService to handle invoice creation upon payment confirmation.
- Modified BookingRepository to support CRUD operations for BookingInvoice.
- Updated TenantDbContext to include BookingInvoice DbSet and relevant configurations.
- Improved error handling and validation for booking completion and payment processes.

Repos/CustomerRepository.cs

@@ -115,6 +115,13 @@ namespace Fitness_core_BE.Repos
                     (l.PrimaryPhoneCached == id || l.EmailCached == id));
         }
 
+        // Staff picking an existing member to link a walk-in booking to (identification only,
+        // see BookingService.CreateGuestBooking/CreateGuestAdhocBooking) -- tenant-scoped by
+        // construction, same as FindActiveLinkByIdentifierAsync above.
+        public Task<TenantCustomerLink?> GetTenantCustomerLinkById(Guid id)
+            => _context.TenantCustomerLink
+                .FirstOrDefaultAsync(l => l.TenantCustomerLinkId == id && l.IsActiveAtThisClient);
+
 
         public async Task<Customer?> UpdateCustomer(Guid customerId, Customer updatedCustomer)
         {