fix: LFO→cutoff modulation, visual knob feedback, persistent hints

- Fix LFO→Filter cutoff: add scaling Gain nodes so LFO (-1..1) maps to
  meaningful Hz modulation (±cutoff value). Same fix for LFO→Osc freq.
  Mod scale updates dynamically when user changes the base param value.
- Visual modulation indicator: knobs receiving LFO/modulation show a
  pulsing dashed ring animation (spin + pulse) around the knob arc
- Persist hint usage per level: using a hint permanently caps that level
  at 2 stars — survives reload/restart. No more cheating by restarting!
- Hint state stored in separate localStorage key (synthquest-hints)
- Admin reset also clears hint history

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

src/game/gameState.js

@@ -61,8 +61,10 @@ export function isLevelUnlocked(levelId, worldLevels) {
 export function resetProgress() {
   _progress = { ...defaultProgress };
   _patches = {};
+  _hints = {};
   saveProgress();
   savePatches();
+  saveHints();
 }
 
 // ==================== Level patch persistence ====================
@@ -105,3 +107,43 @@ export function clearLevelPatch(levelId) {
   delete patches[levelId];
   savePatches();
 }
+
+// ==================== Hint tracking (persisted, no cheating!) ====================
+
+const HINTS_KEY = 'synthquest-hints';
+let _hints = null; // { levelId: true }
+
+function loadHints() {
+  if (_hints) return _hints;
+  try {
+    const raw = localStorage.getItem(HINTS_KEY);
+    _hints = raw ? JSON.parse(raw) : {};
+  } catch {
+    _hints = {};
+  }
+  return _hints;
+}
+
+function saveHints() {
+  if (!_hints) return;
+  try {
+    localStorage.setItem(HINTS_KEY, JSON.stringify(_hints));
+  } catch {}
+}
+
+export function markHintUsed(levelId) {
+  const hints = loadHints();
+  hints[levelId] = true;
+  saveHints();
+}
+
+export function wasHintUsed(levelId) {
+  const hints = loadHints();
+  return !!hints[levelId];
+}
+
+export function clearHintForLevel(levelId) {
+  const hints = loadHints();
+  delete hints[levelId];
+  saveHints();
+}