feat: add clear/limpiar button to sandbox toolbar

Stops audio and removes all modules and connections from the canvas.

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

src/App.jsx

@@ -243,6 +243,12 @@ export default function App({ onSwitchToGame }) {
     emit();
   };
 
+  const handleClearCanvas = () => {
+    if (state.isRunning) stopAudio();
+    deserialize({ modules: [], connections: [] });
+    emit();
+  };
+
   return (
     <div className="app">
       {/* Toolbar */}
@@ -269,6 +275,9 @@ export default function App({ onSwitchToGame }) {
         <button className="toolbar-btn" onClick={handleLoadDemo} style={{ color: 'var(--yellow)' }}>
           🎮 Chiptune Demo
         </button>
+        <button className="toolbar-btn" onClick={handleClearCanvas}>
+          🗑 Limpiar
+        </button>
         <div className="toolbar-sep" />
         <span className="toolbar-label" style={{ color: state.isRunning ? 'var(--green)' : 'var(--text2)' }}>
           {state.isRunning ? '● LIVE' : '○ OFF'}