feat(bookings): dashboard cancellation and waitlist promotion

- POST /v1/catalog/bookings/{id}/cancel lets businesses cancel
  tenant-owned bookings; two-step confirm in the detail modal
- Shared PromoteWaitlist helper promotes earliest waitlisted bookings
  when a class seat frees, on both dashboard and customer cancel paths;
  promoted customers get a confirmation email, waitlist ledger marked
  resolved
- waitlisted status surfaced in bookings UI: stats card, filter, warning
  badge, demo seed, CS+EN strings
- BookingRecord gains created_at for fair ordering; GetBookingByID and
  ResolveWaitlistEntry added to the repository surface

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

apps/backend/openapi/bookra.openapi.yaml

@@ -800,6 +800,26 @@ paths:
           description: Invalid request
         "409":
           description: Conflict with existing booking
+  /v1/catalog/bookings/{bookingID}/cancel:
+    post:
+      tags: [Catalog]
+      operationId: cancelDashboardBooking
+      security:
+        - bearerAuth: []
+      parameters:
+        - in: path
+          name: bookingID
+          required: true
+          schema:
+            type: string
+            format: uuid
+      responses:
+        "200":
+          description: Booking cancelled; freed class seats promote the waitlist
+        "400":
+          description: Booking already cancelled
+        "404":
+          description: Booking not found
   /v1/catalog/blocked-days:
     get:
       tags: [Catalog]