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/commands/sync.rs

@@ -53,7 +53,10 @@ pub async fn sync_queue_mutation(
     );
 
     db_service.execute(query).await.map_err(|e| e.to_string())?;
-    let id = db_service.last_insert_rowid().await.map_err(|e| e.to_string())?;
+    let id = db_service
+        .last_insert_rowid()
+        .await
+        .map_err(|e| e.to_string())?;
 
     Ok(id)
 }
@@ -110,10 +113,7 @@ pub async fn sync_get_pending(
 /// Mark a sync operation as in progress
 #[tauri::command]
 #[specta::specta]
-pub async fn sync_mark_processing(
-    db: State<'_, DatabaseWrapper>,
-    id: i64,
-) -> Result<(), String> {
+pub async fn sync_mark_processing(db: State<'_, DatabaseWrapper>, id: i64) -> Result<(), String> {
     let db_service = {
         let database = db.0.lock().map_err(|e| e.to_string())?;
         Arc::new(database.service())
@@ -131,10 +131,7 @@ pub async fn sync_mark_processing(
 /// Mark a sync operation as completed
 #[tauri::command]
 #[specta::specta]
-pub async fn sync_mark_completed(
-    db: State<'_, DatabaseWrapper>,
-    id: i64,
-) -> Result<(), String> {
+pub async fn sync_mark_completed(db: State<'_, DatabaseWrapper>, id: i64) -> Result<(), String> {
     let db_service = {
         let database = db.0.lock().map_err(|e| e.to_string())?;
         Arc::new(database.service())