Background-audio handoff for video + repository/player refactor

Hand video playback off to a native audio-only stream when the app is
backgrounded or locked, with no on-device video decode (UR-040). Adds
player_enter/exit_background_audio commands, an audio-only stream URL
for video items across the repository layer, and the frontend handoff
state machine wired into VideoPlayer. Includes accompanying
repository/offline/player refactoring and regenerates the traceability
matrix.

src-tauri/src/repository/mod.rs

@@ -1,12 +1,12 @@
-pub mod types;
-pub mod online;
-pub mod offline;
 pub mod hybrid;
+pub mod offline;
+pub mod online;
+pub mod types;
 
-pub use types::*;
-pub use online::{OnlineRepository, JRayActor};
-pub use offline::OfflineRepository;
 pub use hybrid::HybridRepository;
+pub use offline::OfflineRepository;
+pub use online::{JRayActor, OnlineRepository};
+pub use types::*;
 
 use async_trait::async_trait;
 
@@ -242,10 +242,7 @@ pub trait MediaRepository: Send + Sync {
     ///
     /// @req: UR-014 - Make and edit playlists of music that sync back to Jellyfin
     /// @req: JA-019 - Get/create/update playlists
-    async fn get_playlist_items(
-        &self,
-        playlist_id: &str,
-    ) -> Result<Vec<PlaylistEntry>, RepoError>;
+    async fn get_playlist_items(&self, playlist_id: &str) -> Result<Vec<PlaylistEntry>, RepoError>;
 
     /// Add items to a playlist
     ///