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/models.py

@@ -0,0 +1,25 @@
+from django.db import models
+from accounts.models import User
+
+
+class Notification(models.Model):
+    NOTIFICATION_TYPES = [
+        ('event', 'Event'),
+        ('promo', 'Promotion'),
+        ('system', 'System'),
+        ('booking', 'Booking'),
+    ]
+
+    user = models.ForeignKey(User, on_delete=models.CASCADE, related_name='notifications')
+    title = models.CharField(max_length=255)
+    message = models.TextField()
+    notification_type = models.CharField(max_length=20, choices=NOTIFICATION_TYPES, default='system')
+    is_read = models.BooleanField(default=False)
+    action_url = models.URLField(blank=True, null=True)
+    created_at = models.DateTimeField(auto_now_add=True)
+
+    class Meta:
+        ordering = ['-created_at']
+
+    def __str__(self):
+        return f"{self.notification_type}: {self.title} → {self.user.email}"