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/player/timers.rs

@@ -1,5 +1,7 @@
 //! Sleep-timer and autoplay commands.
 //!
+//! TRACES: UR-026, UR-023 | DR-029, DR-047, DR-049
+//!
 //! Thin command adapters over `PlayerController`'s sleep-timer and autoplay
 //! logic, plus persistence of autoplay settings to the database.
 
@@ -7,8 +9,8 @@ use std::sync::Arc;
 use tauri::State;
 
 use super::{
-    create_media_item, get_player_status, DatabaseWrapper, PlayItemRequest, PlayerStatus,
-    PlayerStateWrapper,
+    create_media_item, get_player_status, DatabaseWrapper, PlayItemRequest, PlayerStateWrapper,
+    PlayerStatus,
 };
 use crate::player::{AutoplaySettings, SleepTimerMode, SleepTimerState};
 use crate::storage::db_service::{DatabaseService, Query, QueryParam};
@@ -127,7 +129,9 @@ pub async fn player_play_next_episode(
     let media_item = create_media_item(item, Some(&db)).await?;
 
     let controller = player.0.lock().await;
-    controller.play_item(media_item).map_err(|e| e.to_string())?;
+    controller
+        .play_item(media_item)
+        .map_err(|e| e.to_string())?;
 
     Ok(get_player_status(&controller))
 }
@@ -164,7 +168,10 @@ pub async fn player_on_playback_ended(
             if let Some(repo) = repo {
                 controller.on_video_playback_ended(id, repo).await?
             } else {
-                log::warn!("[Autoplay] No repository available for video autoplay (itemId: {})", id);
+                log::warn!(
+                    "[Autoplay] No repository available for video autoplay (itemId: {})",
+                    id
+                );
                 AutoplayDecision::Stop
             }
         } else {