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/base_socket.py

@@ -0,0 +1,14 @@
+class BaseSocket:
+    upgrade_protocols = ['websocket']
+
+    def __init__(self, server, sid):
+        self.server = server
+        self.sid = sid
+        self.queue = self.server.create_queue()
+        self.last_ping = None
+        self.connected = False
+        self.upgrading = False
+        self.upgraded = False
+        self.closing = False
+        self.closed = False
+        self.session = {}