Add TWP Softphone Flutter app and complete mobile backend API

Backend: Add /voice/token endpoint with AccessToken + VoiceGrant for
mobile VoIP, implement unhold_call() with call leg detection, wire FCM
push notifications into call queue and webhook missed call handlers,
add data-only FCM message support for Android background wake, and add
Twilio API Key / Push Credential settings fields.

Flutter app: Full softphone with Twilio Voice SDK integration, JWT auth
with auto-refresh, SSE real-time queue updates, FCM push notifications,
Material 3 UI with dashboard, active call screen, dialpad, and call
controls (mute/speaker/hold/transfer).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

mobile/lib/models/agent_status.dart

@@ -0,0 +1,38 @@
+enum AgentStatusValue { available, busy, offline }
+
+class AgentStatus {
+  final AgentStatusValue status;
+  final bool isLoggedIn;
+  final String? currentCallSid;
+  final String? lastActivity;
+  final bool availableForQueues;
+
+  AgentStatus({
+    required this.status,
+    required this.isLoggedIn,
+    this.currentCallSid,
+    this.lastActivity,
+    this.availableForQueues = true,
+  });
+
+  factory AgentStatus.fromJson(Map<String, dynamic> json) {
+    return AgentStatus(
+      status: _parseStatus(json['status'] as String),
+      isLoggedIn: json['is_logged_in'] as bool,
+      currentCallSid: json['current_call_sid'] as String?,
+      lastActivity: json['last_activity'] as String?,
+      availableForQueues: json['available_for_queues'] as bool? ?? true,
+    );
+  }
+
+  static AgentStatusValue _parseStatus(String s) {
+    switch (s) {
+      case 'available':
+        return AgentStatusValue.available;
+      case 'busy':
+        return AgentStatusValue.busy;
+      default:
+        return AgentStatusValue.offline;
+    }
+  }
+}

mobile/lib/models/call_info.dart

@@ -0,0 +1,46 @@
+enum CallState { idle, ringing, connecting, connected, disconnected }
+
+class CallInfo {
+  final CallState state;
+  final String? callSid;
+  final String? callerNumber;
+  final Duration duration;
+  final bool isMuted;
+  final bool isSpeakerOn;
+  final bool isOnHold;
+
+  const CallInfo({
+    this.state = CallState.idle,
+    this.callSid,
+    this.callerNumber,
+    this.duration = Duration.zero,
+    this.isMuted = false,
+    this.isSpeakerOn = false,
+    this.isOnHold = false,
+  });
+
+  CallInfo copyWith({
+    CallState? state,
+    String? callSid,
+    String? callerNumber,
+    Duration? duration,
+    bool? isMuted,
+    bool? isSpeakerOn,
+    bool? isOnHold,
+  }) {
+    return CallInfo(
+      state: state ?? this.state,
+      callSid: callSid ?? this.callSid,
+      callerNumber: callerNumber ?? this.callerNumber,
+      duration: duration ?? this.duration,
+      isMuted: isMuted ?? this.isMuted,
+      isSpeakerOn: isSpeakerOn ?? this.isSpeakerOn,
+      isOnHold: isOnHold ?? this.isOnHold,
+    );
+  }
+
+  bool get isActive =>
+      state == CallState.ringing ||
+      state == CallState.connecting ||
+      state == CallState.connected;
+}

mobile/lib/models/queue_state.dart

@@ -0,0 +1,54 @@
+class QueueInfo {
+  final int id;
+  final String name;
+  final String type;
+  final String? extension;
+  final int waitingCount;
+
+  QueueInfo({
+    required this.id,
+    required this.name,
+    required this.type,
+    this.extension,
+    required this.waitingCount,
+  });
+
+  factory QueueInfo.fromJson(Map<String, dynamic> json) {
+    return QueueInfo(
+      id: json['id'] as int,
+      name: json['name'] as String,
+      type: json['type'] as String,
+      extension: json['extension'] as String?,
+      waitingCount: json['waiting_count'] as int,
+    );
+  }
+}
+
+class QueueCall {
+  final String callSid;
+  final String fromNumber;
+  final String toNumber;
+  final int position;
+  final String status;
+  final int waitTime;
+
+  QueueCall({
+    required this.callSid,
+    required this.fromNumber,
+    required this.toNumber,
+    required this.position,
+    required this.status,
+    required this.waitTime,
+  });
+
+  factory QueueCall.fromJson(Map<String, dynamic> json) {
+    return QueueCall(
+      callSid: json['call_sid'] as String,
+      fromNumber: json['from_number'] as String,
+      toNumber: json['to_number'] as String,
+      position: json['position'] as int,
+      status: json['status'] as String,
+      waitTime: json['wait_time'] as int,
+    );
+  }
+}

mobile/lib/models/user.dart

@@ -0,0 +1,22 @@
+class User {
+  final int id;
+  final String login;
+  final String displayName;
+  final String? email;
+
+  User({
+    required this.id,
+    required this.login,
+    required this.displayName,
+    this.email,
+  });
+
+  factory User.fromJson(Map<String, dynamic> json) {
+    return User(
+      id: json['user_id'] as int,
+      login: json['user_login'] as String,
+      displayName: json['display_name'] as String,
+      email: json['email'] as String?,
+    );
+  }
+}