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/copying.py

@@ -0,0 +1,20 @@
+"""Create new instance copies with cooperative ``super()`` calls."""
+
+__all__ = ['CopyBase']
+
+
+class CopyBase:
+    """Create new instance copies with cooperative ``super()`` calls."""
+
+    def copy(self):
+        """Return a copied instance of the object.
+
+        Returns:
+            An independent copy of the current object.
+        """
+        kwargs = self._copy_kwargs()
+        return self.__class__(**kwargs)
+
+    def _copy_kwargs(self, **kwargs):
+        """Return the kwargs to create a copy of the instance."""
+        return kwargs