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

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

notifications/urls.py

@@ -0,0 +1,8 @@
+from django.urls import path
+from .views import NotificationListView, NotificationMarkReadView, NotificationCountView
+
+urlpatterns = [
+    path('list/', NotificationListView.as_view(), name='notification_list'),
+    path('mark-read/', NotificationMarkReadView.as_view(), name='notification_mark_read'),
+    path('count/', NotificationCountView.as_view(), name='notification_count'),
+]