feat(ad_control): new AdSurface + AdPlacement module for placement-based featured/top events

- New ad_control Django app: AdSurface + AdPlacement models with GLOBAL/LOCAL scope
- Admin CRUD API at /api/v1/ad-control/ (JWT-protected): surfaces, placements, picker events
- Placement lifecycle: DRAFT → ACTIVE|SCHEDULED → EXPIRED|DISABLED
- LOCAL scope: Haversine ≤ 50km from event lat/lng (fixed radius, no config needed)
- Consumer APIs: /api/events/featured-events/ and /api/events/top-events/ rewritten
  to use placement-based queries (same URL paths + response shape — no breaking changes)
- Seed command: seed_surfaces --migrate converts existing is_featured/is_top_event booleans
- mount: admin_api/urls.py → ad-control/, mobile_api/urls.py → replaced consumer views
- settings.py: added ad_control to INSTALLED_APPS

ad_control/urls.py

@@ -0,0 +1,18 @@
+from django.urls import path
+from . import views
+
+# Admin CRUD endpoints — mounted at /api/v1/ad-control/
+urlpatterns = [
+    # Surfaces
+    path('surfaces/', views.SurfaceListView.as_view(), name='ad-surfaces'),
+
+    # Placements CRUD
+    path('placements/', views.PlacementListCreateView.as_view(), name='ad-placements'),
+    path('placements/<int:pk>/', views.PlacementDetailView.as_view(), name='ad-placement-detail'),
+    path('placements/<int:pk>/publish/', views.PlacementPublishView.as_view(), name='ad-placement-publish'),
+    path('placements/<int:pk>/unpublish/', views.PlacementUnpublishView.as_view(), name='ad-placement-unpublish'),
+    path('placements/reorder/', views.PlacementReorderView.as_view(), name='ad-placements-reorder'),
+
+    # Events picker
+    path('events/', views.PickerEventsView.as_view(), name='ad-picker-events'),
+]