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/services/core/wsService.ts

@@ -44,6 +44,8 @@ export type WSMessageType =
   | 'call_peer_muted'
   | 'call_invited'
   | 'call_answered_elsewhere'
+  | 'call_participant_joined'
+  | 'call_participant_left'
   | 'sync_required';
 
 export interface WSCallIncomingMessage {
@@ -103,6 +105,19 @@ export interface WSCallAnsweredElsewhereMessage {
   reason?: string;
 }
 
+export interface WSCallParticipantJoinedMessage {
+  type: 'call_participant_joined';
+  call_id: string;
+  user_id: string;
+}
+
+export interface WSCallParticipantLeftMessage {
+  type: 'call_participant_left';
+  call_id: string;
+  user_id: string;
+  reason?: string;
+}
+
 export interface WSErrorMessage {
   type: 'error';
   code: string;
@@ -257,6 +272,8 @@ export type WSMessage =
   | WSCallPeerMutedMessage
   | WSCallInvitedMessage
   | WSCallAnsweredElsewhereMessage
+  | WSCallParticipantJoinedMessage
+  | WSCallParticipantLeftMessage
   | WSErrorMessage
   | WSSyncRequiredMessage;
 
@@ -300,6 +317,9 @@ class WebSocketService {
   private isFallbackMode = false;
   private fallbackCheckTimer: ReturnType<typeof setTimeout> | null = null;
 
+  // 通话中阻止后台断开（对方请求权限等场景会导致 AppState 切换，不应断开 WebSocket）
+  preventDisconnectOnBackground = false;
+
   private getWSUrl(token: string | null): string {
     return `${WS_URL}?token=${encodeURIComponent(token || '')}&compress=1`;
   }
@@ -747,6 +767,14 @@ class WebSocketService {
     this.sendFireAndForget('call_ready', { call_id: callId });
   }
 
+  sendCallGroupInvite(groupId: string, conversationId: string, callType: string): void {
+    this.sendFireAndForget('call_group_invite', {
+      group_id: groupId,
+      conversation_id: conversationId,
+      call_type: callType,
+    });
+  }
+
   private handleMessageSent(payload: any): void {
     // 找到对应的发送请求并resolve
     const pendingMsg = this.pendingMessages.find(p => 
@@ -1059,9 +1087,14 @@ class WebSocketService {
     this.lastAppState = AppState.currentState;
     this.appStateSubscription = AppState.addEventListener('change', (nextState: AppStateStatus) => {
       // 进入后台时断开 WebSocket，由 JPush 负责后台推送通知
+      // 但如果正在通话中则不断开，避免对方请求权限等场景导致通话中断
       if (this.lastAppState === 'active' && nextState.match(/inactive|background/)) {
-        console.log('[WebSocket] App entering background, disconnecting');
-        this.disconnect();
+        if (this.preventDisconnectOnBackground) {
+          console.log('[WebSocket] App entering background but call is active, skipping disconnect');
+        } else {
+          console.log('[WebSocket] App entering background, disconnecting');
+          this.disconnect();
+        }
       }
       // 回到前台时重连 WebSocket
       if (this.lastAppState.match(/inactive|background/) && nextState === 'active' && !this.isConnected()) {