feat(transcoding): add FFmpeg HLS transcoding support

- Introduced `TranscodeManager` for managing on-demand transcoding of local video files.
- Added configuration options for transcoding in `Config` and `LocalFilesConfig`.
- Implemented new API routes for managing transcoding settings, stats, and cache.
- Updated `LocalFilesProvider` to support transcoding capabilities.
- Created frontend components for managing transcode settings and displaying stats.
- Added database migration for transcode settings.
- Enhanced existing routes and DTOs to accommodate new transcoding features.

k-tv-backend/api/src/routes/config.rs

@@ -33,6 +33,7 @@ async fn get_config(State(state): State<AppState>) -> Json<ConfigResponse> {
             search: false,
             streaming_protocol: StreamingProtocol::DirectFile,
             rescan: false,
+            transcode: false,
         });
 
     Json(ConfigResponse {