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/session_state.dart

@@ -9,11 +9,13 @@ import 'package:sync_relay_core/core.dart';
 import '../jellyfin/accounts.dart';
 import '../jellyfin/session_media.dart';
 import '../sfx/sfx.dart';
+import '../sfx/synth_sfx.dart';
 import '../session/health.dart';
 import '../session/session_coordinator.dart';
 import '../widgets/avatar_pipeline.dart';
 import 'connect_prefs.dart';
 import 'server_isolate.dart';
+import 'settings.dart';
 
 enum AppRoute {
   home,
@@ -153,7 +155,10 @@ class SessionState {
   final route = signal(AppRoute.home);
   final recents = signal<List<RecentServer>>(const []);
   final status = signal(const HealthStatus(HealthSeverity.info, 'idle'));
-  final SfxService sfx = const NoopSfxService();
+  final SfxService sfx = SynthSfx(
+    volume: () => AppSettings.instance.soundVolume.peek(),
+    enabled: (k) => !AppSettings.instance.soundsOff.peek().contains(k.name),
+  );
   late final SessionCoordinator coordinator = SessionCoordinator(sfx: sfx);
   final lastForm = ConnectForm();
   JellyfinAccounts get jellyfin => JellyfinAccounts.instance;