Initial release of petkit-monitor

- Monitor real-time status and data of PETKIT smart pet devices.
- Support for feeders (remaining food, feeding history), litter boxes (usage count, cleaning log), water fountains (water level, filter status), and air purifiers.
- Query all or specific device statuses with simple commands.
- Requires PETKIT account credentials in config.json.
- Note: Logging in may log out the mobile app. API is reverse-engineered and may break.