初始化提交

backend/app/db/base.py

@@ -0,0 +1,11 @@
+"""SQLAlchemy declarative base。"""
+
+from sqlalchemy.orm import DeclarativeBase
+
+
+class Base(DeclarativeBase):
+    pass
+
+
+# 导入模型，确保 Alembic autogenerate 能发现 metadata。
+from app import models as _models  # noqa: E402,F401