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/graphviz/parameters/renderers.py

@@ -0,0 +1,70 @@
+"""Rendering renderer parameter handling."""
+
+import typing
+
+from . import base
+
+__all__ = ['RENDERERS', 'verify_renderer', 'Renderer']
+
+RENDERERS = {'cairo',  # $ dot -T:
+             'dot',
+             'fig',
+             'gd',
+             'gdiplus',
+             'map',
+             'pic',
+             'pov',
+             'ps',
+             'svg',
+             'tk',
+             'vml',
+             'vrml',
+             'xdot'}
+
+
+REQUIRED = False
+
+
+def verify_renderer(renderer: typing.Optional[str], *,
+                    required: bool = REQUIRED) -> None:
+    if renderer is None:
+        if required:
+            raise ValueError('missing renderer')
+    elif renderer.lower() not in RENDERERS:
+        raise ValueError(f'unknown renderer: {renderer!r}'
+                         f' (must be None or one of {sorted(RENDERERS)})')
+
+
+class Renderer(base.ParameterBase):
+    """Rendering renderer parameter (no default)."""
+
+    _renderer = None
+
+    _verify_renderer = staticmethod(verify_renderer)
+
+    def __init__(self, *, renderer: typing.Optional[str] = None, **kwargs) -> None:
+        super().__init__(**kwargs)
+
+        self.renderer = renderer
+
+    def _copy_kwargs(self, **kwargs):
+        """Return the kwargs to create a copy of the instance."""
+        renderer = self._getattr_from_dict('_renderer')
+        if renderer is not None:
+            kwargs['renderer'] = renderer
+        return super()._copy_kwargs(**kwargs)
+
+    @property
+    def renderer(self) -> typing.Optional[str]:
+        """The output renderer used for rendering
+            (``'cairo'``, ``'gd'``, ...)."""
+        return self._renderer
+
+    @renderer.setter
+    def renderer(self, renderer: typing.Optional[str]) -> None:
+        if renderer is None:
+            self.__dict__.pop('_renderer', None)
+        else:
+            renderer = renderer.lower()
+            self._verify_renderer(renderer)
+            self._renderer = renderer