feat: Enhance audio management by implementing shutdown procedures on exit

Signed-off-by: Hans Kokx <hans.d.kokx@gmail.com>

apps/wolf_3d_gui/lib/screens/game_screen.dart

@@ -143,6 +143,7 @@ class _GameScreenState extends State<GameScreen> {
       DefaultRendererSettingsPersistence();
   final DefaultSaveGamePersistence _savePersistence =
       DefaultSaveGamePersistence();
+  Future<void>? _audioShutdownFuture;
 
   /// Mirrors [WolfRendererSettings.mode] into the Flutter renderer enum.
   RendererMode _rendererMode = RendererMode.hardware;
@@ -180,7 +181,7 @@ class _GameScreenState extends State<GameScreen> {
         Navigator.of(context).pop();
       },
       onQuit: () {
-        SystemNavigator.pop();
+        unawaited(_quitApplication());
       },
       saveGamePersistence: _savePersistence,
     );
@@ -210,6 +211,31 @@ class _GameScreenState extends State<GameScreen> {
     }
   }
 
+  @override
+  void dispose() {
+    unawaited(_shutdownAudioForExit());
+    super.dispose();
+  }
+
+  Future<void> _quitApplication() async {
+    await _shutdownAudioForExit();
+    await SystemNavigator.pop();
+  }
+
+  Future<void> _shutdownAudioForExit() {
+    final existing = _audioShutdownFuture;
+    if (existing != null) {
+      return existing;
+    }
+
+    final shutdown = () async {
+      await widget.wolf3d.audio.stopAllAudio();
+      widget.wolf3d.audio.dispose();
+    }();
+    _audioShutdownFuture = shutdown;
+    return shutdown;
+  }
+
   @override
   Widget build(BuildContext context) {
     return PopScope(