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

events/migrations/0011_event_contributed_by.py

@@ -0,0 +1,73 @@
+"""
+Add contributed_by field to Event and backfill from overloaded source field.
+
+The admin dashboard stores community contributor identifiers (EVT-XXXXXXXX or email)
+in the source field. This migration:
+1. Adds a dedicated contributed_by CharField
+2. Copies user identifiers from source → contributed_by
+3. Normalizes source back to its intended choices ('eventify', 'community', 'partner')
+"""
+
+from django.db import migrations, models
+
+
+def backfill_contributed_by(apps, schema_editor):
+    """Move user identifiers from source to contributed_by."""
+    Event = apps.get_model('events', 'Event')
+
+    STANDARD_SOURCES = {'eventify', 'community', 'partner', 'eventify_team', 'official', ''}
+
+    for event in Event.objects.all().iterator():
+        source_val = (event.source or '').strip()
+        changed = False
+
+        # User identifier: contains @ (email) or starts with EVT- (eventifyId)
+        if source_val and source_val not in STANDARD_SOURCES and not source_val.startswith('partner:'):
+            event.contributed_by = source_val
+            event.source = 'community'
+            changed = True
+
+        # Normalize eventify_team → eventify
+        elif source_val == 'eventify_team':
+            event.source = 'eventify'
+            changed = True
+
+        # Normalize official → eventify
+        elif source_val == 'official':
+            event.source = 'eventify'
+            changed = True
+
+        if changed:
+            event.save(update_fields=['source', 'contributed_by'])
+
+
+def reverse_backfill(apps, schema_editor):
+    """Reverse: move contributed_by back to source."""
+    Event = apps.get_model('events', 'Event')
+    for event in Event.objects.exclude(contributed_by__isnull=True).exclude(contributed_by='').iterator():
+        event.source = event.contributed_by
+        event.contributed_by = None
+        event.save(update_fields=['source', 'contributed_by'])
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('events', '0010_merge_20260324_1443'),
+    ]
+
+    operations = [
+        # Step 1: Add the field
+        migrations.AddField(
+            model_name='event',
+            name='contributed_by',
+            field=models.CharField(
+                blank=True,
+                help_text='Eventify ID (EVT-XXXXXXXX) or email of the community contributor',
+                max_length=100,
+                null=True,
+            ),
+        ),
+        # Step 2: Backfill data
+        migrations.RunPython(backfill_contributed_by, reverse_backfill),
+    ]