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>

events/migrations/0012_eventlike.py

@@ -0,0 +1,38 @@
+from django.conf import settings
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('events', '0011_event_contributed_by'),
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='EventLike',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('created_at', models.DateTimeField(auto_now_add=True)),
+                ('event', models.ForeignKey(
+                    on_delete=django.db.models.deletion.CASCADE,
+                    related_name='likes',
+                    to='events.event',
+                )),
+                ('user', models.ForeignKey(
+                    on_delete=django.db.models.deletion.CASCADE,
+                    related_name='event_likes',
+                    to=settings.AUTH_USER_MODEL,
+                )),
+            ],
+            options={
+                'unique_together': {('user', 'event')},
+            },
+        ),
+        migrations.AddIndex(
+            model_name='eventlike',
+            index=models.Index(fields=['user', '-created_at'], name='events_even_user_id_created_idx'),
+        ),
+    ]