feat(favorites): add EventLike model, favorites API, and notifications module

- EventLike model (user × event unique constraint, indexed)
- contributed_by field on Event (EVT ID or email of community contributor)
- Favorites API endpoints: toggle-like, my-likes, my-liked-events
- Notifications app wired into main urls.py at /api/notifications/
- accounts migration 0014_merge_0013 (resolves split 0013 branches)
- requirements.txt updated

eventify/urls.py

@@ -36,6 +36,7 @@ urlpatterns = [
     path('banking/', include('banking_operations.urls')),
     path('api/', include('mobile_api.urls')),
     path('api/v1/', include('admin_api.urls')),
+    path('api/notifications/', include('notifications.urls')),
     # path('web-api/', include('web_api.urls')),
 
     path('summernote/', include('django_summernote.urls')),