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.

app/_layout.tsx

@@ -28,6 +28,8 @@ import { useAuthStore } from '../src/stores';
 import { checkForAPKUpdate } from '@/services/platform';
 import { CallScreen, IncomingCallModal, FloatingCallWindow } from '../src/components/call';
 import { jpushService } from '@/services/notification/jpushService';
+import { callKeepService } from '@/services/callkeep';
+import { callStore } from '@/stores/call';
 
 registerNotificationPresentationHandler();
 
@@ -237,6 +239,37 @@ function APKUpdateBootstrap() {
   return null;
 }
 
+function CallKeepBootstrap() {
+  useEffect(() => {
+    if (Platform.OS === 'web') return;
+
+    callKeepService.initialize({
+      onSystemAnswered: () => {
+        callStore.getState().handleSystemAnswer();
+      },
+      onSystemEnded: () => {
+        callStore.getState().endCall('ended');
+      },
+      onSystemMuted: (muted: boolean) => {
+        callStore.getState().handleSystemMuted(muted);
+      },
+      onIncomingCallFromPush: (session) => {
+        callStore.getState().handleIncomingFromPush(session);
+      },
+      onOutgoingStarted: () => {
+        // Outgoing call accepted by system — no action needed,
+        // the WS call_invited / call_accepted flow handles everything
+      },
+    });
+
+    return () => {
+      callKeepService.dispose();
+    };
+  }, []);
+
+  return null;
+}
+
 function ThemedStack() {
   const router = useRouter();
   const resolved = useResolvedColorScheme();
@@ -249,6 +282,7 @@ function ThemedStack() {
       <SessionGate>
         <NotificationBootstrap />
         <APKUpdateBootstrap />
+        <CallKeepBootstrap />
         <Stack screenOptions={{ headerShown: false }}>
           <Stack.Screen name="index" options={{ headerShown: false }} />
           <Stack.Screen name="(auth)" options={{ headerShown: false }} />