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/sfx/sfx.dart

@@ -1,20 +1,22 @@
+/// The app's sounds. Only events that carry news get one: no sound for
+/// what the video itself makes obvious (start, pause, end, seeks).
 enum SfxKind {
+  /// Someone readies up; pitch climbs with [SfxCue.readyIndex].
   ready,
   unready,
+  /// Someone marks everyone ready.
   forceReady,
-  forceUnready,
-  forcePlay,
-  forceHold,
-  kick,
   join,
   leave,
-  stale,
+  kick,
+  /// A new video or episode is put up.
   swap,
-  seek,
-  pause,
-  resume,
   chat,
+  /// Idle warning: auto-unready soon.
   warn,
+  /// The connection to the server dropped / came back.
+  lost,
+  back,
 }
 
 class SfxCue {
@@ -23,42 +25,17 @@ class SfxCue {
   const SfxCue(this.kind, {this.readyIndex = 0});
 }
 
-SfxKind? sfxForFeedAction(String action) {
-  switch (action) {
-    case 'ready':
-      return SfxKind.ready;
-    case 'unready':
-      return SfxKind.unready;
-    case 'force-ready':
-      return SfxKind.forceReady;
-    case 'force-unready':
-      return SfxKind.forceUnready;
-    case 'force-play':
-      return SfxKind.forcePlay;
-    case 'force-hold':
-      return SfxKind.forceHold;
-    case 'kick':
-      return SfxKind.kick;
-    case 'join':
-      return SfxKind.join;
-    case 'leave':
-      return SfxKind.leave;
-    case 'stale':
-      return SfxKind.stale;
-    case 'swap':
-      return SfxKind.swap;
-    case 'seek':
-      return SfxKind.seek;
-    case 'pause':
-      return SfxKind.pause;
-    case 'resume':
-      return SfxKind.resume;
-    case 'chat':
-      return SfxKind.chat;
-    default:
-      return null;
-  }
-}
+SfxKind? sfxForFeedAction(String action) => switch (action) {
+      'ready' => SfxKind.ready,
+      'unready' => SfxKind.unready,
+      'force-ready' => SfxKind.forceReady,
+      'kick' => SfxKind.kick,
+      'join' => SfxKind.join,
+      'leave' => SfxKind.leave,
+      'swap' => SfxKind.swap,
+      'chat' => SfxKind.chat,
+      _ => null,
+    };
 
 abstract class SfxService {
   Future<void> play(SfxCue cue);