feat: add SynthQuest game mode with World 1 (Waves) — 8 puzzle levels

Gamified synth learning inspired by Turing Complete. Progressive puzzle
system teaches oscillators, waveforms, frequency, and mixing through
hands-on module patching. Includes world map, level progression with
3-star rating, target audio playback, solution validation, and
localStorage persistence. Sandbox mode still accessible via button.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/game/gameState.js

@@ -0,0 +1,64 @@
+/**
+ * gameState.js — Game progress persistence
+ * Tracks completed levels, stars earned, and unlocks
+ */
+
+const STORAGE_KEY = 'synthquest-progress';
+
+const defaultProgress = {
+  currentWorld: 'w1',
+  completedLevels: {},  // { levelId: { stars: 3, bestTime: 12.5 } }
+  unlockedWorlds: ['w1'],
+  totalStars: 0,
+};
+
+let _progress = null;
+
+export function loadProgress() {
+  if (_progress) return _progress;
+  try {
+    const raw = localStorage.getItem(STORAGE_KEY);
+    _progress = raw ? { ...defaultProgress, ...JSON.parse(raw) } : { ...defaultProgress };
+  } catch {
+    _progress = { ...defaultProgress };
+  }
+  return _progress;
+}
+
+export function saveProgress() {
+  if (!_progress) return;
+  _progress.totalStars = Object.values(_progress.completedLevels)
+    .reduce((sum, l) => sum + (l.stars || 0), 0);
+  try {
+    localStorage.setItem(STORAGE_KEY, JSON.stringify(_progress));
+  } catch {}
+}
+
+export function completeLevel(levelId, stars) {
+  const p = loadProgress();
+  const existing = p.completedLevels[levelId];
+  if (!existing || stars > existing.stars) {
+    p.completedLevels[levelId] = { stars, completedAt: Date.now() };
+  }
+  saveProgress();
+}
+
+export function getLevelProgress(levelId) {
+  const p = loadProgress();
+  return p.completedLevels[levelId] || null;
+}
+
+export function isLevelUnlocked(levelId, worldLevels) {
+  const p = loadProgress();
+  // First level is always unlocked
+  const idx = worldLevels.findIndex(l => l.id === levelId);
+  if (idx === 0) return true;
+  // Previous level must have at least 1 star
+  const prevId = worldLevels[idx - 1]?.id;
+  return prevId && p.completedLevels[prevId]?.stars >= 1;
+}
+
+export function resetProgress() {
+  _progress = { ...defaultProgress };
+  saveProgress();
+}