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

admin_api/urls.py

@@ -1,4 +1,4 @@
-from django.urls import path
+from django.urls import path, include
 from rest_framework_simplejwt.views import TokenRefreshView
 from . import views
 
@@ -74,4 +74,7 @@ urlpatterns = [
     path('rbac/scopes/', views.ScopeListView.as_view(), name='rbac-scope-list'),
     path('rbac/org-tree/', views.OrgTreeView.as_view(), name='rbac-org-tree'),
     path('rbac/audit-log/', views.AuditLogListView.as_view(), name='rbac-audit-log'),
+
+    # Ad Control
+    path('ad-control/', include('ad_control.urls')),
 ]