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/state.rs

@@ -28,6 +28,12 @@ pub struct AppState {
     /// Index for the local-files provider, used by the rescan route.
     #[cfg(feature = "local-files")]
     pub local_index: Option<Arc<infra::LocalIndex>>,
+    /// TranscodeManager for FFmpeg HLS transcoding (requires TRANSCODE_DIR).
+    #[cfg(feature = "local-files")]
+    pub transcode_manager: Option<Arc<infra::TranscodeManager>>,
+    /// SQLite pool for transcode settings CRUD.
+    #[cfg(feature = "local-files")]
+    pub sqlite_pool: Option<sqlx::SqlitePool>,
 }
 
 impl AppState {
@@ -110,6 +116,10 @@ impl AppState {
             config: Arc::new(config),
             #[cfg(feature = "local-files")]
             local_index: None,
+            #[cfg(feature = "local-files")]
+            transcode_manager: None,
+            #[cfg(feature = "local-files")]
+            sqlite_pool: None,
         })
     }
 }