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

backend/app/models/site.py

@@ -0,0 +1,21 @@
+import uuid
+from datetime import datetime
+
+from sqlalchemy import Boolean, DateTime, ForeignKey, String, func
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.db.base_class import Base
+
+
+class Site(Base):
+    __tablename__ = "sites"
+
+    id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    study_id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), ForeignKey("studies.id"), index=True, nullable=False)
+    name: Mapped[str] = mapped_column(String(200), nullable=False)
+    city: Mapped[str | None] = mapped_column(String(100), nullable=True)
+    pi_name: Mapped[str | None] = mapped_column(String(100), nullable=True)
+    contact: Mapped[str | None] = mapped_column(String(100), nullable=True)
+    is_active: Mapped[bool] = mapped_column(Boolean, nullable=False, server_default="true")
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), nullable=False, server_default=func.now())