Deactivate button for the 3D effect

'Disattiva' in the Animazioni 3D tab restores the last non-3D preset
(tracked by applyEffect), answering 'how do I turn the 3D output off'
without hunting through the effect library.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/control.html

@@ -158,9 +158,14 @@
           <select id="glb-effect-fam"></select>
           <select id="glb-effect-preset"></select>
         </div>
-        <button id="glb-effect-go" class="wide">▶ Attiva sull'output</button>
+        <div class="row">
+          <button id="glb-effect-go">▶ Attiva sull'output</button>
+          <button id="glb-effect-off">⏹ Disattiva (torna agli effetti)</button>
+        </div>
         <div class="hint-mini">Le famiglie 3D vivono qui (non più nella libreria Effetti):
-          “Modello 3D” balla da solo a tempo; le “Interattivo” usano la camera.</div>
+          “Modello 3D” balla da solo a tempo; le “Interattivo” usano la camera.
+          “Disattiva” ripristina l'ultimo effetto normale (equivale a scegliere
+          un preset dal tab Effetti).</div>
       </section>
       <section class="span2">
         <label>Modello 3D (GLB)</label>

src/control.js

@@ -8,8 +8,10 @@ const filePath = (f) => djv.pathForFile(f);
 // ---------------------------------------------------------------- effects
 const EFFECTS = window.EFFECTS;
 let currentEffect = EFFECTS.list[0];
+let lastNon3d = EFFECTS.list[0];   // to step back out of the 3D families
 
 function applyEffect(effect) {
+  if (!effect.isModel3d && !effect.isInteractive) lastNon3d = effect;
   currentEffect = effect;
   send({ type: 'effect', effect });
   $('#scene-name').textContent = effect.name;
@@ -354,6 +356,7 @@ fill3dPresets();
 fam3dSel.addEventListener('change', () => { fill3dPresets(); apply3d(); });
 pre3dSel.addEventListener('change', apply3d);
 $('#glb-effect-go').addEventListener('click', apply3d);
+$('#glb-effect-off').addEventListener('click', () => applyEffect(lastNon3d));
 
 $('#btn-glb-load').addEventListener('click', () => $('#glb-input').click());
 $('#glb-input').addEventListener('change', async (e) => {