feat: admin mode, worlds 4-6, and stereo output fix

- Admin panel: add/remove stars, unlock worlds, reset progress (🛠 button)
- World 4 "Modulación" (8 levels): vibrato, sirena, wah-wah, auto-pan, FM, wobble bass
- World 5 "Efectos" (8 levels): delay, slapback, reverb, distortion, dub echo, shoegaze, ambient
- World 6 "Diseño Sonoro" (8 levels): kick, hi-hat, snare, pad, reese bass, laser, trance arp, final boss
- Star unlock progression: W4=36★, W5=48★, W6=60★ (total 48 levels, 144 stars)
- Fix stereo output: left/right channels now route through Tone.Merge for true stereo separation

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

src/game/WorldMap.jsx

@@ -2,9 +2,12 @@ import React from 'react';
 import { WORLD_1 } from './levels/world1.js';
 import { WORLD_2 } from './levels/world2.js';
 import { WORLD_3 } from './levels/world3.js';
+import { WORLD_4 } from './levels/world4.js';
+import { WORLD_5 } from './levels/world5.js';
+import { WORLD_6 } from './levels/world6.js';
 import { getLevelProgress, isLevelUnlocked, loadProgress } from './gameState.js';
 
-const worlds = [WORLD_1, WORLD_2, WORLD_3];
+const worlds = [WORLD_1, WORLD_2, WORLD_3, WORLD_4, WORLD_5, WORLD_6];
 
 function Stars({ count, max = 3 }) {
   return (
@@ -30,7 +33,7 @@ function isWorldUnlocked(world) {
   return getTotalStars() >= world.unlockStars;
 }
 
-export default function WorldMap({ onSelectLevel, onSandbox }) {
+export default function WorldMap({ onSelectLevel, onSandbox, onAdmin }) {
   const totalStars = getTotalStars();
   const maxStars = getMaxStars();
 
@@ -52,6 +55,11 @@ export default function WorldMap({ onSelectLevel, onSandbox }) {
           <button className="gm-sandbox-btn" onClick={onSandbox}>
             🎛 Sandbox
           </button>
+          {onAdmin && (
+            <button className="gm-admin-btn" onClick={onAdmin} title="Admin Mode">
+              🛠
+            </button>
+          )}
         </div>
       </div>