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/output.html

@@ -47,6 +47,7 @@
   <script src="effects.js"></script>
   <script src="fluid.js"></script>
   <script src="interactive.js"></script>
+  <script src="model3d.js"></script>
   <script src="visualizer.js"></script>
   <script src="audio.js"></script>
   <script src="output.js"></script>