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>

DTOs/Booking/BookingRequests.cs

@@ -25,7 +25,7 @@ namespace Fitness_core_BE.DTOs.Booking
         public Guid? CustomerId { get; set; }
     }
 
-    public class CreateAdhocBookingRequest
+    public class CreateWalkInBookingRequest
     {
         [Required]
         public Guid FacilityId { get; set; }
@@ -39,7 +39,7 @@ namespace Fitness_core_BE.DTOs.Booking
         public int? PartySize { get; set; }
     }
 
-    public class CreateGuestAdhocBookingRequest
+    public class CreateGuestWalkInBookingRequest
     {
         [Required]
         public Guid FacilityId { get; set; }
@@ -98,7 +98,7 @@ namespace Fitness_core_BE.DTOs.Booking
         public string OtpCode { get; set; } = string.Empty;
 
         /// <summary>Picked from the club's managed RFID tag pool (GET api/client/rfid-tags?
-        /// status=Available) -- never free-typed. Required in practice for an AdHoc booking's
+        /// status=Available) -- never free-typed. Required in practice for a WalkIn booking's
         /// check-in; optional for Scheduled bookings that don't hand out a physical tag.</summary>
         public Guid? RfidTagId { get; set; }
     }
@@ -115,14 +115,14 @@ namespace Fitness_core_BE.DTOs.Booking
         public string? GuestPhone { get; set; }
     }
 
-    /// <summary>Exactly one shape applies, matching the booking's current BookingMode: AdHoc
+    /// <summary>Exactly one shape applies, matching the booking's current BookingMode: WalkIn
     /// bookings move within the SAME facility to a new StartTime/DurationMinutes; Scheduled
     /// bookings move to a different FacilitySession (also on the same facility). Only allowed
     /// while the booking is still Confirmed, and only onto a slot with room -- re-runs the same
     /// availability check as creation, excluding the booking's own current slot.</summary>
     public class RescheduleBookingRequest
     {
-        // AdHoc reschedule.
+        // WalkIn reschedule.
         public DateTime? StartTime { get; set; }
         [Range(1, int.MaxValue, ErrorMessage = "DurationMinutes must be at least 1")]
         public int? DurationMinutes { get; set; }