Update app.py

Remove preprocessing and unused imports from app.py

Add device tracking and active device override to backend and receiver.

Fix ThinkingConfig validation error

Integrate Gemini API for image rotation detection

Implement buffered image queue for asynchronous uploads

Fix: Re-apply Mailbox logic to app.py and push

Implement Mailbox (Poll-based) Image Relay system

Initial commit with preprocessing and base64 forwarding