chore: 添加虚拟环境到仓库

- 添加 backend_service/venv 虚拟环境
- 包含所有Python依赖包
- 注意：虚拟环境约393MB，包含12655个文件

backend_service/venv/lib/python3.13/site-packages/fastapi/cli.py

@@ -0,0 +1,13 @@
+try:
+    from fastapi_cli.cli import main as cli_main
+
+except ImportError:  # pragma: no cover
+    cli_main = None  # type: ignore
+
+
+def main() -> None:
+    if not cli_main:  # type: ignore[truthy-function]
+        message = 'To use the fastapi command, please install "fastapi[standard]":\n\n\tpip install "fastapi[standard]"\n'
+        print(message)
+        raise RuntimeError(message)  # noqa: B904
+    cli_main()