Sprint 1: polish — sound, pause, tutorial, touch UI

- SoundManager via Web Audio API (no asset files needed) with procedural
  SFX for jump, spring, powerup, stomp, break, death, milestone, new-best
- Sound persists mute state in localStorage; mute button on Menu and Game
- Pause system: ESC key or onscreen pause button, modal overlay with
  Resume and Main Menu options, physics correctly paused/resumed
- First-run tutorial overlay explaining controls and platform types,
  dismissed and remembered via localStorage flag
- Touch indicator hints fade after 3.5s on touch devices only
- Menu start triggers AudioContext initialization (browser autoplay rules)
- GameOverScene supports ENTER/SPACE shortcut for retry, NEW BEST text
  now pulses, sounds fire on each transition

src/managers/SoundManager.js

@@ -0,0 +1,131 @@
+class SoundManager {
+  constructor() {
+    this.ctx = null;
+    this.master = null;
+    this.muted = false;
+    this.musicNodes = null;
+
+    const raw = localStorage.getItem('naddie_muted');
+    this.muted = raw === '1';
+  }
+
+  init() {
+    if (this.ctx) return;
+    const AC = window.AudioContext || window.webkitAudioContext;
+    if (!AC) return;
+    this.ctx = new AC();
+    this.master = this.ctx.createGain();
+    this.master.gain.value = 0.4;
+    this.master.connect(this.ctx.destination);
+  }
+
+  resume() {
+    if (this.ctx && this.ctx.state === 'suspended') {
+      this.ctx.resume();
+    }
+  }
+
+  setMuted(value) {
+    this.muted = value;
+    localStorage.setItem('naddie_muted', value ? '1' : '0');
+    if (this.master) {
+      this.master.gain.value = value ? 0 : 0.4;
+    }
+  }
+
+  isMuted() {
+    return this.muted;
+  }
+
+  _beep(freq, duration, type = 'square', volume = 0.3) {
+    if (!this.ctx || this.muted) return;
+    const osc = this.ctx.createOscillator();
+    const gain = this.ctx.createGain();
+    osc.type = type;
+    osc.frequency.setValueAtTime(freq, this.ctx.currentTime);
+    gain.gain.setValueAtTime(volume, this.ctx.currentTime);
+    gain.gain.exponentialRampToValueAtTime(0.001, this.ctx.currentTime + duration);
+    osc.connect(gain);
+    gain.connect(this.master);
+    osc.start();
+    osc.stop(this.ctx.currentTime + duration);
+  }
+
+  _sweep(freqStart, freqEnd, duration, type = 'square', volume = 0.3) {
+    if (!this.ctx || this.muted) return;
+    const osc = this.ctx.createOscillator();
+    const gain = this.ctx.createGain();
+    osc.type = type;
+    osc.frequency.setValueAtTime(freqStart, this.ctx.currentTime);
+    osc.frequency.exponentialRampToValueAtTime(Math.max(1, freqEnd), this.ctx.currentTime + duration);
+    gain.gain.setValueAtTime(volume, this.ctx.currentTime);
+    gain.gain.exponentialRampToValueAtTime(0.001, this.ctx.currentTime + duration);
+    osc.connect(gain);
+    gain.connect(this.master);
+    osc.start();
+    osc.stop(this.ctx.currentTime + duration);
+  }
+
+  _noise(duration, volume = 0.15) {
+    if (!this.ctx || this.muted) return;
+    const bufferSize = this.ctx.sampleRate * duration;
+    const buffer = this.ctx.createBuffer(1, bufferSize, this.ctx.sampleRate);
+    const data = buffer.getChannelData(0);
+    for (let i = 0; i < bufferSize; i++) {
+      data[i] = (Math.random() * 2 - 1) * (1 - i / bufferSize);
+    }
+    const src = this.ctx.createBufferSource();
+    src.buffer = buffer;
+    const gain = this.ctx.createGain();
+    gain.gain.value = volume;
+    src.connect(gain);
+    gain.connect(this.master);
+    src.start();
+  }
+
+  jump() {
+    this._sweep(320, 540, 0.1, 'square', 0.14);
+  }
+
+  land() {
+    this._beep(180, 0.06, 'triangle', 0.10);
+  }
+
+  spring() {
+    this._sweep(280, 1000, 0.18, 'square', 0.22);
+    setTimeout(() => this._sweep(800, 1300, 0.12, 'triangle', 0.15), 50);
+  }
+
+  powerup() {
+    [440, 554, 659, 880].forEach((f, i) => setTimeout(() => this._beep(f, 0.13, 'triangle', 0.20), i * 55));
+  }
+
+  stomp() {
+    this._sweep(420, 100, 0.16, 'sawtooth', 0.22);
+    this._noise(0.08, 0.10);
+  }
+
+  break() {
+    this._noise(0.15, 0.12);
+    this._sweep(200, 60, 0.2, 'sawtooth', 0.10);
+  }
+
+  death() {
+    this._sweep(280, 50, 0.5, 'sawtooth', 0.28);
+    setTimeout(() => this._noise(0.3, 0.15), 100);
+  }
+
+  milestone() {
+    [523, 659, 783, 1046].forEach((f, i) => setTimeout(() => this._beep(f, 0.22, 'triangle', 0.25), i * 90));
+  }
+
+  click() {
+    this._beep(660, 0.05, 'square', 0.12);
+  }
+
+  newBest() {
+    [523, 659, 783, 1046, 1318].forEach((f, i) => setTimeout(() => this._beep(f, 0.18, 'triangle', 0.25), i * 80));
+  }
+}
+
+export const sound = new SoundManager();