When ensureChatAvailable fails for expert mode, the error message
previously used chatStatusMessage which shows "聊天服务已就绪" when
the runtime/gateway are healthy — misleading the user when the real
issue is project-level readiness (projectReady=false or missing
currentProjectId).

Now the error message identifies the actual failure:
- 项目工作区未就绪 when projectReady is false
- 未选择项目 when currentProjectId is missing
- 本地运行时未就绪 when runtime is not running
- 网关未连接 when gateway is not connected
- Falls back to the original chatStatusMessage for uncovered cases
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>