Replace the custom WebRTC implementation with LiveKit for improved
stability and feature support.
- Remove `react-native-webrtc` and custom `WebRTCManager`
- Implement `LiveKitService` for room and track management
- Update `callStore` to handle LiveKit events and connection states
- Refactor `CallScreen` (mobile and web) to use `@livekit/react-native`
and `VideoView`
- Update WebSocket protocol to use `call_ready` instead of manual SDP/ICE
exchanges
- Add necessary camera and microphone permissions to `app.json`
- Update Metro and Babel configurations for LiveKit compatibility
