chore: remove dead code to eliminate all compiler warnings

- Remove unused get_artist() (replaced by get_artist_page())
- Remove unused Format::label(), Format::all()
- Remove unused QwsTokenResponse and QwsToken structs
- Remove unused PlayerCommand::Seek (seeking uses atomics directly)
- Remove unused PlayerState::Stopped, TrackInfo::format
- Remove unused PlayerStatus::get_current_track()

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

rust/src/player/decoder.rs

@@ -195,11 +195,6 @@ pub fn play_track_inline(
                     paused.store(false, Ordering::SeqCst);
                     *status.state.lock().unwrap() = super::PlayerState::Playing;
                 }
-                Ok(PlayerCommand::Seek(s)) => {
-                    status.seek_target_secs.store(s, Ordering::Relaxed);
-                    status.seek_requested.load(Ordering::SeqCst); // read-side fence
-                    status.seek_requested.store(true, Ordering::SeqCst);
-                }
                 Ok(PlayerCommand::SetVolume(v)) => {
                     status.volume.store(v, Ordering::Relaxed);
                 }