fix: should use app_name instead of req.app_name

Co-authored-by: Yifan Wang <wanyif@google.com>
PiperOrigin-RevId: 908883116

Author: wyf7107

src/google/adk/cli/adk_web_server.py

@@ -2091,7 +2091,7 @@ async def run_agent_live(
         return
 
       await websocket.accept()
-      self.current_app_name_ref.value = req.app_name
+      self.current_app_name_ref.value = app_name
       runner_for_context = await self.get_runner_async(app_name)
       _set_telemetry_context_if_needed(runner_for_context)