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/exceptions.py

@@ -0,0 +1,31 @@
+"""Commonly used exception classes."""
+
+from .backend.execute import ExecutableNotFound, CalledProcessError
+
+__all__ = ['ExecutableNotFound', 'CalledProcessError',
+           'RequiredArgumentError', 'FileExistsError',
+           'UnknownSuffixWarning', 'FormatSuffixMismatchWarning',
+           'DotSyntaxWarning']
+
+
+class RequiredArgumentError(TypeError):
+    """:exc:`TypeError` raised if a required argument is missing."""
+
+
+class FileExistsError(FileExistsError):
+    """:exc:`FileExistsError` raised with ``raise_if_exists=True``."""
+
+
+class UnknownSuffixWarning(RuntimeWarning):
+    """:exc:`RuntimeWarning` raised if the suffix of ``outfile`` is unknown
+        and the given ``format`` is used instead."""
+
+
+class FormatSuffixMismatchWarning(UserWarning):
+    """:exc:`UserWarning` raised if the suffix ``outfile``
+        does not match the given ``format``."""
+
+
+class DotSyntaxWarning(RuntimeWarning):
+    """:exc:`RuntimeWarning` raised if a quoted string
+        is expected to cause a ``CalledProcessError`` from rendering."""