fix(player): stop engine before dropping ALSA stream on format change

In the Play and PlayStreaming handlers, the old engine's writer thread
still holds an Arc<AlsaDirectStream> when the stream_opt is dropped and
a new snd_pcm_open() is attempted. This causes EBUSY on track switches
with sample rate changes. Reorder to: stop engine -> drop stream -> open
new stream, matching the Stop handler's correct lifecycle.

cc

crates/qbz-player/src/player/mod.rs

@@ -1145,8 +1145,18 @@ impl Player {
                                     } else {
                                         log::info!("Creating initial audio stream");
                                     }
-                                    // Drop old stream
+                                    // Stop engine FIRST so its writer thread releases its
+                                    // Arc<AlsaDirectStream> reference before we drop the stream.
+                                    // Without this, snd_pcm_open() races against the old PCM
+                                    // handle and fails with EBUSY.
+                                    if let Some(engine) = current_engine.take() {
+                                        engine.stop();
+                                        std::thread::sleep(Duration::from_millis(50));
+                                    }
+                                    // Now this drop is the last Arc ref — PCM actually closes
                                     drop(stream_opt.take());
+                                    // Give kernel time to fully release the ALSA device
+                                    std::thread::sleep(Duration::from_millis(50));
                                 }
 
                                 log::info!(
@@ -1585,7 +1595,18 @@ impl Player {
                                         mode
                                     );
                                     }
+                                    // Stop engine FIRST so its writer thread releases its
+                                    // Arc<AlsaDirectStream> reference before we drop the stream.
+                                    // Without this, snd_pcm_open() races against the old PCM
+                                    // handle and fails with EBUSY.
+                                    if let Some(engine) = current_engine.take() {
+                                        engine.stop();
+                                        std::thread::sleep(Duration::from_millis(50));
+                                    }
+                                    // Now this drop is the last Arc ref — PCM actually closes
                                     drop(stream_opt.take());
+                                    // Give kernel time to fully release the ALSA device
+                                    std::thread::sleep(Duration::from_millis(50));
                                 }
 
                                 let stream_result = if let Some(settings) =