Refactor user account system and remove moderation integration

- Remove first_name and last_name fields from User model
- Add user deletion and social provider services
- Restructure auth serializers into separate directory
- Update avatar upload functionality and API endpoints
- Remove django-moderation integration documentation
- Add mandatory compliance enforcement rules
- Update frontend documentation with API usage examples

backend/apps/accounts/selectors.py

@@ -176,8 +176,7 @@ def user_search_autocomplete(*, query: str, limit: int = 10) -> QuerySet:
     """
     return User.objects.filter(
         Q(username__icontains=query)
-        | Q(first_name__icontains=query)
-        | Q(last_name__icontains=query),
+        | Q(display_name__icontains=query),
         is_active=True,
     ).order_by("username")[:limit]