Chat: Add chat session restore and busy state; clean up code

- Add "Start New Chat" button and support for restoring previous chat sessions with thread id
- Display prompt to continue or reset previous sessions on page load
- Introduce chat busy state to prevent race conditions; disable UI controls during chat operations
- Remove unnecessary functions for arming/disarming vehicle
- Enhance parameter metadata loading
- Clean up labels, error handling, and general code structure

Author: esatiyev