fix(player): lockscreen skip scrubs instead of advancing in background audio

onSkipToNext/onSkipToPrevious forwarded a bare next/previous to Rust, which
always advanced the queue. Correct for music, wrong for a video whose audio is
running through a background-audio handoff (UR-040): pressing skip to re-hear a
line jumped to the next episode instead of scrubbing.

resolve_skip_action in player/seek.rs maps the command to Advance or SeekTo, and
is_background_audio_active() is the whole test — the handoff exists only for
video, and an episode played through it reports MediaType::Audio, so media type
cannot distinguish the case. Forward 30s, back 10s, both clamped to [0, duration]
so a skip near either end cannot seek negative or read as EOF and advance.

Routed through the same spawn-then-seek_absolute path as the scrubber, because a
handoff seek re-opens the stream and must not run under the blocking lock
(DR-159). Kotlin keeps sending the opaque command; it only gains FAST_FORWARD/
REWIND in the PlaybackStateCompat so the system stops drawing skip arrows for a
control that scrubs. The remote-volume action block is deliberately untouched:
the handoff never applies to cast sessions, where skip really does mean advance.

Tests written first and watched fail (left: Advance, right: SeekTo). 706 Rust
tests pass, clippy 0, coverage 90%.

src-tauri/src/lib.rs

@@ -314,6 +314,10 @@ use download::DownloadManager;
 use jellyfin::{HttpClient, HttpConfig};
 #[cfg(target_os = "android")]
 use playback_mode::PlaybackModeManager;
+// Only the Android MediaSessionHandler resolves lockscreen skips; on other
+// targets this would be an unused import.
+#[cfg(target_os = "android")]
+use player::seek::{resolve_skip_action, SkipAction};
 use player::{MediaSessionManager, PlayerBackend, PlayerController, TauriEventEmitter};
 // NullBackend is used both for platforms without a native backend AND as a graceful
 // fallback when a native backend (MPV/ExoPlayer) fails to initialize, so the app can
@@ -449,14 +453,55 @@ impl MediaSessionHandler {
             return;
         }
 
+        // Skip means different things depending on what is actually playing, so
+        // the decision belongs here rather than in the Kotlin that drew the
+        // button: music advances the queue, while a video whose audio is running
+        // through a background-audio handoff scrubs instead (UR-040). Routed
+        // through the same spawn-and-seek path as "seek:" above, because
+        // `seek_absolute` rebuilds the stream during a handoff and must not run
+        // under the blocking lock (DR-159).
+        //
+        // TRACES: UR-040, UR-006 | DR-201
+        if command == "next" || command == "previous" {
+            let is_next = command == "next";
+            let player = self.player.clone();
+            tokio::spawn(async move {
+                let controller = player.lock().await;
+                let action = resolve_skip_action(
+                    is_next,
+                    controller.is_background_audio_active(),
+                    controller.position(),
+                    controller.duration(),
+                );
+                let label = if is_next { "next" } else { "previous" };
+                let result: Result<(), String> = match action {
+                    SkipAction::Advance => if is_next {
+                        controller.next()
+                    } else {
+                        controller.previous()
+                    }
+                    .map_err(|e| e.to_string()),
+                    SkipAction::SeekTo(position) => {
+                        info!(
+                            "[MediaSession] Background audio: '{}' scrubs to {:.1}s",
+                            label, position
+                        );
+                        controller.seek_absolute(position).await
+                    }
+                };
+                if let Err(e) = result {
+                    error!("[MediaSession] Skip '{}' failed: {}", label, e);
+                }
+            });
+            return;
+        }
+
         // Use blocking_lock since this is called from a non-async JNI callback
         let controller = self.player.blocking_lock();
 
         let result = match command {
             "play" => controller.play(),
             "pause" => controller.pause(),
-            "next" => controller.next(),
-            "previous" => controller.previous(),
             "stop" => controller.stop(),
             _ => {
                 warn!("[MediaSession] Unknown command: {}", command);