feat: add electron GUI wrapper for backend service

[hjyssg]

Summary

• add a new packages/backend_gui Electron + React application that wraps the existing backend service
• implement configuration persistence, process lifecycle management, log streaming/rotation, health checks, and tray controls in the main process
• build a Tailwind-based UI for configuration, service control, and log filtering plus provide packaging scripts, README, and a smoke test helper

Testing

• not run (environment only)

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https://chatgpt.com/codex/tasks/task_e_68d9f4b1dd0c83259cc2513bbef30bd9

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

[P1] Stop backend before quitting Electron app

The quit handlers call stopHealthChecks() and app.quit() without shutting down the child process managed by ServiceManager. If the user closes the GUI while the backend is running, the spawned server keeps running in the background and continues to hold the port, defeating the purpose of the GUI wrapper. The tray “退出” item uses the same pattern a few lines above. Consider awaiting serviceManager.stop() (or otherwise killing the child) before quitting so the backend terminates with the application.

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