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/test/sfx_test.dart

@@ -0,0 +1,59 @@
+import 'dart:math' as math;
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:watch_together/src/sfx/sfx.dart';
+import 'package:watch_together/src/sfx/sound_bank.dart';
+import 'package:watch_together/src/sfx/synth.dart';
+
+double _pitch(List<double> x, int from) {
+  final c = <double>[];
+  for (var l = 0; l < 700; l++) {
+    var s = 0.0;
+    for (var i = from; i < from + 2048; i++) {
+      s += x[i] * x[i + l];
+    }
+    c.add(s);
+  }
+  var best = 0.0, lag = 0.0;
+  for (var l = 30; l < 699; l++) {
+    if (c[l] > best && c[l] >= c[l - 1] && c[l] >= c[l + 1]) {
+      best = c[l];
+      lag = l + (c[l - 1] - c[l + 1]) / (2 * (c[l - 1] - 2 * c[l] + c[l + 1]));
+    }
+  }
+  return sampleRate / lag;
+}
+
+void main() {
+  test('every sound is described, quiet, short and clean', () {
+    for (final k in SfxKind.values) {
+      expect(soundInfo[k], isNotNull, reason: k.name);
+      final r = render(soundFor(k));
+      final peak = r.fold<double>(0, (m, v) => math.max(m, v.abs()));
+      expect(20 * math.log(peak) / math.ln10, lessThanOrEqualTo(-16.9), reason: '${k.name} peak');
+      expect(r.length / sampleRate, lessThan(3), reason: '${k.name} length');
+      expect(r.every((v) => v.isFinite), isTrue, reason: k.name);
+      expect(r.first.abs() + r.last.abs(), lessThan(1e-3), reason: '${k.name} clicks');
+    }
+  });
+
+  test('the ready ladder climbs and stays in range', () {
+    expect(render(readySound(0)), render(readySound(1)));
+    expect(render(readySound(99)), render(readySound(6)));
+  });
+
+  test('koto strings are in tune', () {
+    for (final hz in [293.66, 587.33, 880.0, 1174.66]) {
+      final r = render(SoundSpec([Note(0, hz, 1.0)], room: 0, cutoff: 20000));
+      final cents = 1200 * math.log(_pitch(r, 2000) / hz) / math.ln2;
+      expect(cents.abs(), lessThan(5), reason: '$hz');
+    }
+  });
+
+  test('wav header and length', () {
+    final b = wav(render(soundFor(SfxKind.chat)));
+    expect(String.fromCharCodes(b.sublist(0, 4)), 'RIFF');
+    expect(String.fromCharCodes(b.sublist(8, 12)), 'WAVE');
+    expect(b.length, 44 + render(soundFor(SfxKind.chat)).length * 2);
+  });
+}