Add MediaType and MediaPurpose to model exports

MediaType and MediaPurpose have been added to the `__all__` exports in the `models` module. This ensures they are properly exposed for import and use throughout the application.

backend/app/models/__init__.py

@@ -34,7 +34,7 @@ from .activity_log import ActivityLog, ActivityType
 __all__ = [
     'Base', 'TimestampMixin', 'UUIDMixin',
     'User',
-    'Event', 'EventManager', 'EventManagerRole', 'EventTheme', 'EventMedia',
+    'Event', 'EventManager', 'EventManagerRole', 'EventTheme', 'EventMedia','MediaType', 'MediaPurpose',
     'Guest', 'GuestStatus', 'RSVP', 'RSVPStatus',
     'GiftItem', 'GiftStatus', 'GiftPriority', 'GiftCategory', 'GiftPurchase',
     'EmailTemplate', 'TemplateType',