Sounds: Japanese-house sound set in the app, layout demo removed

Eleven sounds for events that carry news (ready, unready, everyone ready,
join, leave, kick, new video, others' chat, idle warning, connection
lost/back); none for what the video already says. New voices: koto
(Karplus-Strong, bendable), furin chime, rin bowl, bamboo, hyoshigi,
shoji slide, in the Yo scale on D. Played by SynthSfx at the Settings
volume with per-sound switches and previews. The debug layout mock is
gone.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/desktop/lib/src/state/settings.dart

@@ -20,6 +20,8 @@ const _keyAutoAdvance = 'autoAdvance';
 const _keyMpvControls = 'mpvControls';
 const _keyHideReReleases = 'hideReReleases';
 const _keyProgressLine = 'progressLine';
+const _keySoundVolume = 'soundVolume';
+const _keySoundsOff = 'soundsOff';
 
 enum HwdecMode { auto, off, custom }
 
@@ -40,6 +42,10 @@ class AppSettings {
   /// A 2 px progress line at the bottom of the video while the controls
   /// are hidden (both designs). Applies live.
   final progressLine = signal(true);
+  /// App sounds (`sfx/`): 0..1, 0 = silent.
+  final soundVolume = signal(0.5);
+  /// `SfxKind` names switched off one by one.
+  final soundsOff = signal<Set<String>>(const {});
 
   /// Video shaders: one choice, used on join and changed both here and
   /// in the session (Ctrl+0..6, the shader button).
@@ -82,6 +88,10 @@ class AppSettings {
       if (hideRe is bool) hideReReleases.value = hideRe;
       final line = box.get(_keyProgressLine);
       if (line is bool) progressLine.value = line;
+      final vol = box.get(_keySoundVolume);
+      if (vol is num) soundVolume.value = vol.toDouble().clamp(0, 1);
+      final off = box.get(_keySoundsOff);
+      if (off is List) soundsOff.value = Set.unmodifiable(off.whereType<String>());
       final preset = box.get(_keyShaderPreset);
       shaderPreset.value =
           ShaderPreset.values.where((p) => p.name == preset).firstOrNull ??
@@ -129,6 +139,16 @@ class AppSettings {
     _put(_keyProgressLine, on);
   }
 
+  void setSoundVolume(double v) {
+    soundVolume.value = v.clamp(0, 1);
+    _put(_keySoundVolume, soundVolume.value);
+  }
+
+  void setSoundOn(String kind, bool on) {
+    soundsOff.value = Set.unmodifiable(on ? ({...soundsOff.value}..remove(kind)) : {...soundsOff.value, kind});
+    _put(_keySoundsOff, soundsOff.value.toList());
+  }
+
   void setHideReReleases(bool on) {
     hideReReleases.value = on;
     _put(_keyHideReReleases, on);