Modello 3D family: audio-reactive GLB model renderer

New model3d.js: minimal GLB loader (JSON+BIN chunks, accessors with
byteStride, node hierarchy baked into vertices, embedded PNG/JPEG base
colour textures) and a WebGL2 renderer on the shared canvas — palette
fill light, beat-pulsing fresnel rim, treble speculars, bass breathing
via normal displacement, orbiting camera auto-fitted to the bounding
box, gradient backdrop with a bass glow. A generated torus knot shows
before any GLB is loaded. 'Carica un modello .glb' button in the SVG
section; the path persists and is re-sent when the output restarts.

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

src/control.html

@@ -127,6 +127,10 @@
         <button id="btn-svg-load" class="wide">📂 Carica un SVG/immagine…</button>
         <input type="file" id="svg-input" accept="image/svg+xml,image/*" hidden />
         <div class="hint-mini">Scegli una sagoma → diventa un effetto reattivo. Per cambiare colori/stile filtra la libreria su “SVG/Immagine”.</div>
+        <label>Modello 3D (GLB)</label>
+        <button id="btn-glb-load" class="wide">🧊 Carica un modello .glb…</button>
+        <input type="file" id="glb-input" accept=".glb" hidden />
+        <div class="hint-mini" id="glb-name">Il modello ruota a tempo di musica nella famiglia “Modello 3D”.</div>
       </section>
 
       <section class="span2" id="effect-seq-section">