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/dashscope/protocol/websocket.py

@@ -0,0 +1,30 @@
+# Copyright (c) Alibaba, Inc. and its affiliates.
+
+
+class WebsocketStreamingMode:
+    # TODO how to know request is duplex or other.
+    NONE = 'none'  # no stream
+    IN = 'in'  # stream in
+    OUT = 'out'
+    DUPLEX = 'duplex'
+
+
+ACTION_KEY = 'action'
+EVENT_KEY = 'event'
+HEADER = 'header'
+TASK_ID = 'task_id'
+ERROR_NAME = 'error_code'
+ERROR_MESSAGE = 'error_message'
+
+
+class EventType:
+    STARTED = 'task-started'
+    GENERATED = 'result-generated'
+    FINISHED = 'task-finished'
+    FAILED = 'task-failed'
+
+
+class ActionType:
+    START = 'run-task'
+    CONTINUE = 'continue-task'
+    FINISHED = 'finish-task'