feat(video): 事务化切换与前端统一编排，增强视频输入格式支持

- 后端：切换事务+transition_id，/stream/mode 返回 switching/transition_id 与实际 codec

- 事件：新增 mode_switching/mode_ready，config/webrtc_ready/mode_changed 关联事务

- 编码/格式：扩展 NV21/NV16/NV24/RGB/BGR 输入与转换链路，RKMPP direct input 优化

- 前端：useVideoSession 统一切换，失败回退真实切回 MJPEG，菜单格式同步修复

- 清理：useVideoStream 降级为 MJPEG-only

libs/hwcodec/cpp/common/ffmpeg_ffi.h

@@ -14,11 +14,15 @@
 enum AVPixelFormat {
   AV_PIX_FMT_YUV420P = 0,
   AV_PIX_FMT_YUYV422 = 1,
+  AV_PIX_FMT_RGB24 = 2,
+  AV_PIX_FMT_BGR24 = 3,
   AV_PIX_FMT_YUV422P = 4,     // planar YUV 4:2:2
   AV_PIX_FMT_YUVJ420P = 12,   // JPEG full-range YUV420P (same layout as YUV420P)
   AV_PIX_FMT_YUVJ422P = 13,   // JPEG full-range YUV422P (same layout as YUV422P)
   AV_PIX_FMT_NV12 = 23,
   AV_PIX_FMT_NV21 = 24,
+  AV_PIX_FMT_NV16 = 101,
+  AV_PIX_FMT_NV24 = 188,
 };
 
 int av_log_get_level(void);
@@ -26,4 +30,4 @@ void av_log_set_level(int level);
 void hwcodec_set_av_log_callback();
 void hwcodec_set_flag_could_not_find_ref_with_poc();
 
-#endif
+#endif