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/engineio/json.py

@@ -0,0 +1,16 @@
+"""JSON-compatible module with sane defaults."""
+
+from json import *  # noqa: F401, F403
+from json import loads as original_loads
+
+
+def _safe_int(s):
+    if len(s) > 100:
+        raise ValueError('Integer is too large')
+    return int(s)
+
+
+def loads(*args, **kwargs):
+    if 'parse_int' not in kwargs:  # pragma: no cover
+        kwargs['parse_int'] = _safe_int
+    return original_loads(*args, **kwargs)