Sounds: three presets (Cosmic, Abyss, Wood & glass), chosen overall or per sound; nudge sound

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

apps/desktop/lib/src/sfx/sfx.dart

@@ -17,6 +17,8 @@ enum SfxKind {
   /// The connection to the server dropped / came back.
   lost,
   back,
+  /// Someone pokes you for attention; plays only on your end.
+  nudge,
 }
 
 class SfxCue {