Facility booking-mode redesign, multi-plan subscriptions, and Classes

Implements the facility-classes-booking-dashboard plan (backend):

- Facility.BookingMode (single Scheduled/AdHoc choice) replaced with
  independent SupportsClasses/SupportsBooking flags, so one facility
  can run a class and accept walk-in bookings; a running class now
  blocks walk-in booking for its window on both create and reschedule.
- CustomerPlan.GrantsGymAccess + CustomerPlanClass join table let a
  customer hold one gym-access plan plus any number of class-only
  plans. Replaced the old single-subscription resolution
  (GetActiveSubscriptionByCustomerId/HasAnyActiveSubscriptionAsync)
  with gym-access-aware and class-aware resolvers across booking
  creation/cancellation, plan assignment, and customer self-service.
  Fixed ChangeMembershipPlan/renewal plan-changes, which resolved "the
  subscription to replace" by most-recent-created and would have
  deactivated a member's class subscription instead of their gym one.
- New FacilityClass model: recurring class definitions (Daily/Weekly/
  Monthly/Custom) with lazy occurrence generation (8-week horizon,
  race-safe via a unique index) and proper unlimited-capacity handling.
  "Mark not held" replaces the old bare-cancel: cascades to cancel and
  refund every confirmed booking on the occurrence through the same
  core CancelBooking uses, and frees the slot for walk-in booking.
  Scheduling conflicts (a walk-in booking now overlapping a class) are
  surfaced for staff to resolve via the existing Reschedule flow.
- Renamed the pre-existing "AdHoc" booking-mode terminology to
  "WalkIn" throughout (routes, methods, DTOs, the stored BookingMode
  value) for a clearer, simpler name.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Controllers/BookingController.cs

@@ -34,9 +34,9 @@ namespace Fitness_core_BE.Controllers
 
         [CustomMiddleware]
         [TenantResolution]
-        [HttpPost("api/app/bookings/adhoc")]
-        public async Task<ActionResult<ApiResponse<object>>> CreateMemberAdhocBooking([FromBody] CreateAdhocBookingRequest request)
-            => Response(await _bookingService.CreateMemberAdhocBooking(new
+        [HttpPost("api/app/bookings/walkin")]
+        public async Task<ActionResult<ApiResponse<object>>> CreateMemberWalkInBooking([FromBody] CreateWalkInBookingRequest request)
+            => Response(await _bookingService.CreateMemberWalkInBooking(new
             {
                 facilityId = request.FacilityId,
                 startTime = request.StartTime.ToString("o"),
@@ -70,9 +70,9 @@ namespace Fitness_core_BE.Controllers
             }, HttpContext));
 
         [AllowAnonymous]
-        [HttpPost("api/public/bookings/guest/adhoc")]
-        public async Task<ActionResult<ApiResponse<object>>> CreateGuestAdhocBooking([FromBody] CreateGuestAdhocBookingRequest request)
-            => Response(await _bookingService.CreateGuestAdhocBooking(new
+        [HttpPost("api/public/bookings/guest/walkin")]
+        public async Task<ActionResult<ApiResponse<object>>> CreateGuestWalkInBooking([FromBody] CreateGuestWalkInBookingRequest request)
+            => Response(await _bookingService.CreateGuestWalkInBooking(new
             {
                 facilityId = request.FacilityId,
                 startTime = request.StartTime.ToString("o"),