feat(call): implement CallKeep integration and enhance group call support

Integrate `expo-callkit-telecom` to support native system call handling (answering, ending, and muting via system UI). This includes a new `callKeepService` and a `CallKeepBootstrap` component to manage the lifecycle of system call events.

Additionally, improves the calling experience by:
- Adding support for group calls with participant tracking and UI indicators.
- Enhancing LiveKit integration by replacing polling with event-driven video track synchronization.
- Updating `WebSocketService` to prevent disconnection when the app enters the background during an active call.
- Adding new WebSocket message types for participant join/leave events and group invites.
- Refining call UI components (`CallScreen`, `FloatingCallWindow`, `IncomingCallModal`) for better visual feedback and safe area handling.

Refactor LiveKit service to use event-driven updates for local and remote tracks, improving performance and reliability.

src/components/call/CallScreen.tsx

@@ -40,10 +40,27 @@ const CallScreen: React.FC = () => {
   const [remoteVideoTrack, setRemoteVideoTrack] = useState<VideoTrack | null>(null);
   const [localVideoTrack, setLocalVideoTrack] = useState<VideoTrack | null>(null);
 
-  // Subscribe to LiveKit track events
+  // Event-driven video track subscription (no polling)
   useEffect(() => {
     const unsubs: (() => void)[] = [];
 
+    // Sync current tracks immediately
+    const syncTracks = () => {
+      const lp = liveKitService.localParticipant;
+      if (lp) {
+        const videoPub = lp.getTrackPublication(Track.Source.Camera);
+        setLocalVideoTrack((videoPub?.track as VideoTrack | undefined) ?? null);
+      }
+      liveKitService.remoteParticipants.forEach((participant) => {
+        const videoPub = participant.getTrackPublication(Track.Source.Camera);
+        if (videoPub?.track) {
+          setRemoteVideoTrack(videoPub.track as VideoTrack);
+        }
+      });
+    };
+    syncTracks();
+
+    // Remote video track events
     unsubs.push(
       liveKitService.on('trackSubscribed', ({ track }) => {
         if (track.kind === Track.Kind.Video) {
@@ -69,28 +86,32 @@ const CallScreen: React.FC = () => {
     );
 
     unsubs.push(
-      liveKitService.on('trackUnmuted', ({ publication, participant }) => {
+      liveKitService.on('trackUnmuted', ({ publication }) => {
         if (publication.source === Track.Source.Camera && publication.track) {
           setRemoteVideoTrack(publication.track as VideoTrack);
         }
       })
     );
 
-    // Poll local video track from localParticipant
-    const localPollInterval = setInterval(() => {
-      const lp = liveKitService.localParticipant;
-      if (lp) {
-        const videoPub = lp.getTrackPublication(Track.Source.Camera);
-        const track = (videoPub?.track ?? null) as VideoTrack | null;
-        setLocalVideoTrack((prev) => (prev === track ? prev : track));
-      } else {
-        setLocalVideoTrack((prev) => (prev === null ? prev : null));
-      }
-    }, 500);
+    // Local video track events (replace 500ms polling)
+    unsubs.push(
+      liveKitService.on('localTrackPublished', ({ publication }) => {
+        if (publication.source === Track.Source.Camera && publication.track) {
+          setLocalVideoTrack(publication.track as VideoTrack);
+        }
+      })
+    );
+
+    unsubs.push(
+      liveKitService.on('localTrackUnpublished', ({ publication }) => {
+        if (publication.source === Track.Source.Camera) {
+          setLocalVideoTrack(null);
+        }
+      })
+    );
 
     return () => {
       unsubs.forEach((unsub) => unsub());
-      clearInterval(localPollInterval);
     };
   }, []);