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

src/video/mod.rs

@@ -18,11 +18,15 @@ pub mod video_session;
 pub use capture::VideoCapturer;
 pub use convert::{PixelConverter, Yuv420pBuffer};
 pub use device::{VideoDevice, VideoDeviceInfo};
-pub use encoder::{JpegEncoder, H264Encoder, H264EncoderType};
+pub use encoder::{H264Encoder, H264EncoderType, JpegEncoder};
 pub use format::PixelFormat;
 pub use frame::VideoFrame;
 pub use h264_pipeline::{H264Pipeline, H264PipelineBuilder, H264PipelineConfig};
-pub use shared_video_pipeline::{EncodedVideoFrame, SharedVideoPipeline, SharedVideoPipelineConfig, SharedVideoPipelineStats};
+pub use shared_video_pipeline::{
+    EncodedVideoFrame, SharedVideoPipeline, SharedVideoPipelineConfig, SharedVideoPipelineStats,
+};
 pub use stream_manager::VideoStreamManager;
 pub use streamer::{Streamer, StreamerState};
-pub use video_session::{VideoSessionManager, VideoSessionManagerConfig, VideoSessionInfo, VideoSessionState, CodecInfo};
+pub use video_session::{
+    CodecInfo, VideoSessionInfo, VideoSessionManager, VideoSessionManagerConfig, VideoSessionState,
+};