Step 3：Study / Site / StudyMember + 项目权限

backend/app/models/user.py

@@ -5,7 +5,7 @@ from sqlalchemy import Boolean, DateTime, String, func
 from sqlalchemy.dialects.postgresql import UUID
 from sqlalchemy.orm import Mapped, mapped_column
 
-from app.db.base import Base
+from app.db.base_class import Base
 
 
 class User(Base):