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/storage/db_service.rs

@@ -128,7 +128,9 @@ impl DatabaseService for RusqliteService {
     async fn execute(&self, query: Query) -> DbResult<usize> {
         let conn = Arc::clone(&self.conn);
         tokio::task::spawn_blocking(move || {
-            let conn = conn.lock().map_err(|e| format!("Failed to lock connection: {}", e))?;
+            let conn = conn
+                .lock()
+                .map_err(|e| format!("Failed to lock connection: {}", e))?;
             execute_query(&conn, query)
         })
         .await
@@ -139,7 +141,9 @@ impl DatabaseService for RusqliteService {
         let conn = Arc::clone(&self.conn);
         let sql = sql.to_string();
         tokio::task::spawn_blocking(move || {
-            let conn = conn.lock().map_err(|e| format!("Failed to lock connection: {}", e))?;
+            let conn = conn
+                .lock()
+                .map_err(|e| format!("Failed to lock connection: {}", e))?;
             conn.execute_batch(&sql)
                 .map_err(|e| format!("Execute batch failed: {}", e))
         })
@@ -154,7 +158,9 @@ impl DatabaseService for RusqliteService {
     {
         let conn = Arc::clone(&self.conn);
         tokio::task::spawn_blocking(move || {
-            let conn = conn.lock().map_err(|e| format!("Failed to lock connection: {}", e))?;
+            let conn = conn
+                .lock()
+                .map_err(|e| format!("Failed to lock connection: {}", e))?;
             query_one(&conn, query, mapper)
         })
         .await
@@ -168,7 +174,9 @@ impl DatabaseService for RusqliteService {
     {
         let conn = Arc::clone(&self.conn);
         tokio::task::spawn_blocking(move || {
-            let conn = conn.lock().map_err(|e| format!("Failed to lock connection: {}", e))?;
+            let conn = conn
+                .lock()
+                .map_err(|e| format!("Failed to lock connection: {}", e))?;
             query_optional(&conn, query, mapper)
         })
         .await
@@ -182,7 +190,9 @@ impl DatabaseService for RusqliteService {
     {
         let conn = Arc::clone(&self.conn);
         tokio::task::spawn_blocking(move || {
-            let conn = conn.lock().map_err(|e| format!("Failed to lock connection: {}", e))?;
+            let conn = conn
+                .lock()
+                .map_err(|e| format!("Failed to lock connection: {}", e))?;
             query_many(&conn, query, mapper)
         })
         .await
@@ -196,7 +206,9 @@ impl DatabaseService for RusqliteService {
     {
         let conn = Arc::clone(&self.conn);
         tokio::task::spawn_blocking(move || {
-            let conn = conn.lock().map_err(|e| format!("Failed to lock connection: {}", e))?;
+            let conn = conn
+                .lock()
+                .map_err(|e| format!("Failed to lock connection: {}", e))?;
 
             conn.execute("BEGIN TRANSACTION", [])
                 .map_err(|e| format!("Failed to begin transaction: {}", e))?;
@@ -224,7 +236,9 @@ impl DatabaseService for RusqliteService {
     async fn last_insert_rowid(&self) -> DbResult<i64> {
         let conn = Arc::clone(&self.conn);
         tokio::task::spawn_blocking(move || {
-            let conn = conn.lock().map_err(|e| format!("Failed to lock connection: {}", e))?;
+            let conn = conn
+                .lock()
+                .map_err(|e| format!("Failed to lock connection: {}", e))?;
             Ok(conn.last_insert_rowid())
         })
         .await
@@ -255,7 +269,9 @@ where
 {
     match query_one(conn, query, mapper) {
         Ok(value) => Ok(Some(value)),
-        Err(e) if e.contains("Query returned no rows") || e.contains("QueryReturnedNoRows") => Ok(None),
+        Err(e) if e.contains("Query returned no rows") || e.contains("QueryReturnedNoRows") => {
+            Ok(None)
+        }
         Err(e) => Err(e),
     }
 }
@@ -325,10 +341,7 @@ mod tests {
         let service = RusqliteService::new(Arc::new(Mutex::new(conn)));
 
         let query = Query::new("SELECT name FROM test WHERE id = 1");
-        let name: String = service
-            .query_one(query, |row| row.get(0))
-            .await
-            .unwrap();
+        let name: String = service.query_one(query, |row| row.get(0)).await.unwrap();
 
         assert_eq!(name, "Bob");
     }
@@ -346,10 +359,7 @@ mod tests {
         let service = RusqliteService::new(Arc::new(Mutex::new(conn)));
 
         let query = Query::new("SELECT name FROM test ORDER BY id");
-        let names: Vec<String> = service
-            .query_many(query, |row| row.get(0))
-            .await
-            .unwrap();
+        let names: Vec<String> = service.query_many(query, |row| row.get(0)).await.unwrap();
 
         assert_eq!(names, vec!["Alice", "Bob"]);
     }