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/_defaults.py

@@ -0,0 +1,70 @@
+"""Set package-wide default parameters and IPython/Jupyter display format."""
+
+__all_ = ['DEFAULT_SOURCE_EXTENSION',
+          'set_default_engine', 'set_default_format', 'set_jupyter_format']
+
+DEFAULT_SOURCE_EXTENSION = 'gv'
+
+
+def set_default_engine(engine: str) -> str:
+    """Change the default ``engine`` and return the old default value.
+
+    Args:
+        engine: new default ``engine``
+            used by all present and newly created instances
+            without explicitly set ``engine``
+            (``'dot'``, ``'neato'``, ...).
+
+    Returns:
+        The old default value used for ``engine``.
+    """
+    from . import parameters
+
+    parameters.verify_engine(engine)
+
+    old_default_engine = parameters.Parameters._engine
+    parameters.Parameters._engine = engine
+    return old_default_engine
+
+
+def set_default_format(format: str) -> str:
+    """Change the default ``format`` and return the old default value.
+
+    Args:
+        format: new default ``format``
+            used by all present and newly created instances
+            without explicitly set ``format``
+            (``'pdf'``, ``'png'``, ...).
+
+    Returns:
+        The old default value used for ``format``.
+    """
+    from . import parameters
+
+    parameters.verify_format(format)
+
+    old_default_format = parameters.Parameters._format
+    parameters.Parameters._format = format
+    return old_default_format
+
+
+def set_jupyter_format(jupyter_format: str) -> str:
+    """Change the default mimetype format for ``_repr_mimebundle_()`` and return the old value.
+
+    Args:
+        jupyter_format: new default IPython/Jupyter display format
+            used by all present and newly created instances
+            (``'svg'``, ``'png'``, ...).
+
+    Returns:
+        The old default value used for IPython/Jupyter display format.
+    """
+    from . import jupyter_integration
+
+    mimetype = jupyter_integration.get_jupyter_format_mimetype(jupyter_format)
+
+    old_mimetype = jupyter_integration.JupyterIntegration._jupyter_mimetype
+    old_format = jupyter_integration.get_jupyter_mimetype_format(old_mimetype)
+
+    jupyter_integration.JupyterIntegration._jupyter_mimetype = mimetype
+    return old_format