fix(player): return from background audio onto the episode it advanced to

An episode that ends while backgrounded in audio-only mode advances in the
backend, but player_exit_background_audio returned only a position, so the
video page reloaded the episode it was mounted with -- the previous one, at
the new episode's timestamp.

The command now returns BackgroundAudioResume { itemId, positionSeconds }.
planHandoffReturn yields "other-item" when the id differs from the mounted
one, and the player page navigates to that episode with resumeAt=<seconds>,
marking the outgoing episode watched and suppressing its stale stop report.

TRACES: UR-040, UR-023 | DR-296 | UT-265, UT-266

src/lib/components/player/VideoPlayer.svelte

@@ -120,6 +120,12 @@
     onNext?: () => void; // Called when user clicks next episode button
     hasNext?: boolean; // Whether there is a next episode available
     isLive?: boolean; // Live stream (Live TV) - no seek bar, no resume, no progress reporting
+    /**
+     * Returning from background audio found the backend on a different item
+     * (the episode advanced while backgrounded). The page switches to it; this
+     * player must not reload the one it was mounted with. (DR-296)
+     */
+    onResumeOtherItem?: (itemId: string, positionSeconds: number) => void;
   }
 
   let {
@@ -137,6 +143,7 @@
     onNext,
     hasNext = false,
     isLive = false,
+    onResumeOtherItem,
   }: Props = $props();
 
   // The id this player instance reports progress against. Snapshotted from the
@@ -2035,9 +2042,12 @@
     const wasPlaying = shouldResumeOnForeground(handoffState.wasPlaying, get(playerState).kind);
     handoffState = { ...initialHandoffState };
     try {
-      // Absolute position the native audio reached (base offset applied in Rust).
-      const pos = await commands.playerExitBackgroundAudio();
-      log.debug("Returning from background audio at:", pos.toFixed(1));
+      // The item the native audio is on and the absolute position it reached
+      // (base offset applied in Rust). The item may not be `media`: an episode
+      // that ended while backgrounded has already advanced in the backend.
+      const resume = await commands.playerExitBackgroundAudio();
+      const pos = resume.positionSeconds;
+      log.debug("Returning from background audio at:", pos.toFixed(1), "item:", resume.itemId);
 
       isMediaReady = false;
       // The foreground seek below (pendingForegroundSeek/handleCanPlay) OWNS the
@@ -2056,8 +2066,18 @@
         position: pos,
         wasPlaying,
         nativeStateKind: get(playerState).kind,
+        mountedItemId: media?.id ?? null,
+        resumeItemId: resume.itemId,
       });
 
+      // Reloading `media` here would bring back the previous episode at the new
+      // one's timestamp. Hand the switch to the page instead.
+      // TRACES: UR-040, UR-023 | DR-296
+      if (plan.target === "other-item" && plan.itemId) {
+        onResumeOtherItem?.(plan.itemId, plan.position);
+        return;
+      }
+
       pendingForegroundPlay = plan.shouldPlay;
 
       // Determine the target stream + how the element/offset should be