feat:摄像头选择，副屏页面修改

lib/common/utils/plugs/face_discern_plugs.dart

@@ -142,6 +142,25 @@ abstract class FaceDiscernPlugs {
     return _invokeRecognizeConfiguration('resetRecognizeConfiguration');
   }
 
+  /// 枚举终端摄像头并逐一做预览帧色度探测；探测需短暂打开摄像头，耗时数秒。
+  static Future<TerminalCameraSelection> getCameraChoices() async {
+    final map = await _channel.invokeMethod<dynamic>('getCameraChoices');
+    if (map is! Map) throw StateError('原生未返回有效的摄像头列表');
+    return TerminalCameraSelection.fromMap(map);
+  }
+
+  /// 保存人工选择的识别摄像头；-1 恢复自动选择。空闲时立即生效，识别中延迟到会话结束。
+  static Future<void> setCameraSelection(int cameraId) async {
+    await _channel.invokeMethod<void>('setCameraSelection', {
+      'cameraId': cameraId,
+    });
+  }
+
+  /// 只读当前人工选择的识别摄像头编号；-1 表示自动，不触发摄像头探测。
+  static Future<int> getCameraSelection() async {
+    return await _channel.invokeMethod<int>('getCameraSelection') ?? -1;
+  }
+
   static Stream<FaceRecognitionSessionEvent> get sessionStream {
     _sessionStream ??= _sessionEventChannel
         .receiveBroadcastStream()