feat(call): migrate from WebRTC to LiveKit

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

app.json

@@ -16,6 +16,7 @@
       "supportsTablet": true,
       "infoPlist": {
         "NSMicrophoneUsageDescription": "允许威友访问您的麦克风以进行语音通话",
+        "NSCameraUsageDescription": "允许威友访问您的相机以进行视频通话",
         "UIBackgroundModes": [
           "fetch",
           "remote-notification",
@@ -41,6 +42,7 @@
       "permissions": [
         "VIBRATE",
         "RECORD_AUDIO",
+        "CAMERA",
         "RECEIVE_BOOT_COMPLETED",
         "WAKE_LOCK",
         "READ_EXTERNAL_STORAGE",
@@ -138,6 +140,7 @@
         }
       ],
       "expo-font",
+      "@livekit/react-native",
       [
         "expo-notifications",
         {