feat(audio): audio output device selection (closes #169)

Adds the ability to choose which audio output device Psysonic plays
through — useful for USB DACs, dedicated soundcards, and multi-device setups.

Rust (audio.rs):
- open_stream_for_device_and_rate(device_name, rate): opens a named
  device by cpal name, falls back to system default if not found
- AudioEngine.selected_device: persists the chosen device across
  stream reopens so hi-res rate switches stay on the right device
- audio_list_devices: Tauri command — returns all output device names
- audio_set_device: Tauri command — switches device immediately,
  drops old sinks, emits audio:device-changed
- start_device_watcher: now handles two cases:
    1. No pinned device + system default changed → reopen on new default
    2. Pinned device disappeared (DAC unplugged) → clear selected_device,
       fall back to system default, emit audio:device-reset

Frontend:
- authStore: audioOutputDevice (string | null), persisted
- playerStore: applies stored device on cold start
- App.tsx: listens to audio:device-reset, clears authStore device
  and restarts playback on the fallback device
- Settings → Audio tab: device dropdown at top (above Hi-Res and EQ),
  uses CustomSelect (portal-based, styled), all 8 locales
- CustomSelect: added disabled prop

Note: exclusive mode (WASAPI exclusive, CoreAudio exclusive) is out
of scope for now.

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

src/App.tsx

@@ -437,6 +437,26 @@ function TauriEventBridge() {
     return () => { unlisten?.(); };
   }, []);
 
+  // Pinned output device was unplugged — Rust already fell back to system default.
+  // Clear the stored device so the Settings dropdown resets to "System Default".
+  useEffect(() => {
+    let unlisten: (() => void) | undefined;
+    listen('audio:device-reset', () => {
+      useAuthStore.getState().setAudioOutputDevice(null);
+      const { currentTrack, currentTime, isPlaying, playTrack, resetAudioPause } = usePlayerStore.getState();
+      if (!currentTrack) return;
+      if (isPlaying) {
+        const pos = currentTime;
+        const dur = currentTrack.duration || 1;
+        playTrack(currentTrack);
+        setTimeout(() => usePlayerStore.getState().seek(pos / dur), 600);
+      } else {
+        resetAudioPause();
+      }
+    }).then(u => { unlisten = u; });
+    return () => { unlisten?.(); };
+  }, []);
+
   // Sync tray-icon visibility with the user's stored setting.
   // Runs once on mount (initial sync) and again whenever the setting changes.
   const showTrayIcon = useAuthStore(s => s.showTrayIcon);