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/httptools/parser/protocol.py

@@ -0,0 +1,15 @@
+from typing import Protocol
+
+
+class HTTPProtocol(Protocol):
+    """Used for providing static type-checking when parsing through the http protocol"""
+
+    def on_message_begin() -> None: ...
+    def on_url(url: bytes) -> None: ...
+    def on_header(name: bytes, value: bytes) -> None: ...
+    def on_headers_complete() -> None: ...
+    def on_body(body: bytes) -> None: ...
+    def on_message_complete() -> None: ...
+    def on_chunk_header() -> None: ...
+    def on_chunk_complete() -> None: ...
+    def on_status(status: bytes) -> None: ...