- Updated `.env.example` to include `BROWSER_INACTIVITY_TIMEOUT` for auto-cleanup of inactive sessions.
- Enhanced `cli.py` to load the new inactivity timeout configuration into environment variables.
- Added background thread functionality in `browser_tool.py` to periodically clean up inactive browser sessions based on the configured timeout.
- Improved session management by tracking last activity timestamps and ensuring cleanup occurs when sessions exceed inactivity limits.