fix issue

app/database.py

@@ -50,9 +50,15 @@ async_session_factory = async_sessionmaker(
 async def get_db() -> AsyncGenerator[AsyncSession, None]:
     """
     FastAPI 依赖项：获取异步数据库会话。
+    请求正常结束后自动 commit，异常时自动 rollback。
     """
     async with async_session_factory() as session:
-        yield session
+        try:
+            yield session
+            await session.commit()
+        except Exception:
+            await session.rollback()
+            raise
 
 
 async def close_db() -> None: