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/referencing/_attrs.pyi

@@ -0,0 +1,21 @@
+from collections.abc import Callable
+from typing import Any, TypeVar
+
+from attr import attrib, field
+
+class UnsupportedSubclassing(Exception): ...
+
+_T = TypeVar("_T")
+
+def __dataclass_transform__(
+    *,
+    frozen_default: bool = False,
+    field_descriptors: tuple[type | Callable[..., Any], ...] = ...,
+) -> Callable[[_T], _T]: ...
+@__dataclass_transform__(field_descriptors=(attrib, field))
+def define(cls: type[_T]) -> type[_T]: ...
+@__dataclass_transform__(
+    frozen_default=True,
+    field_descriptors=(attrib, field),
+)
+def frozen(cls: type[_T]) -> type[_T]: ...