feat: Wahab demo prep — Cancelled status, phone persistence, admin delete, users picker, detail-page fixes

- Add Cancelled as terminal status reachable from all active states; exclude
  from SLA breach reporting and dashboard active counts; add to status pickers
- Persist customer phone on ticket create/update (was silently dropped);
  add tickets.phone migration + legacy self-heal guard
- Add admin-only DELETE /api/tickets/{id} (removes timeline/photos/escalations)
- Add GET /api/auth/users for the assign-technician dropdown (was hardcoded)
- TicketOut now returns nested unit/category so the detail page stops showing
  '—' for Unit/Property/Category
- Ticket numbering uses max+1 so deletions never re-issue a number
- New-issue form: require Category and (standard mode) Priority client-side
- Tests: 11 new cases covering cancellation, SLA exemption, phone, delete,
  users endpoint, numbering

app/templates/base.html

@@ -51,6 +51,7 @@
         .status-wahab-review { @apply bg-violet-100 text-violet-800; }
         .status-closed { @apply bg-gray-200 text-gray-600; }
         .status-reopened { @apply bg-pink-100 text-pink-800; }
+        .status-cancelled { @apply bg-gray-300 text-gray-700 line-through; }
         .priority-urgent { @apply bg-red-100 text-red-800 border-red-300; }
         .priority-high { @apply bg-orange-100 text-orange-800 border-orange-300; }
         .priority-medium { @apply bg-yellow-100 text-yellow-800 border-yellow-300; }
@@ -318,7 +319,8 @@
                         'on-field verification': 'status-on-field-verification',
                         'wahab review': 'status-wahab-review',
                         'closed': 'status-closed',
-                        'reopened': 'status-reopened'
+                        'reopened': 'status-reopened',
+                        'cancelled': 'status-cancelled'
                     };
                     return map[status.toLowerCase()] || 'bg-gray-100 text-gray-800';
                 },