Per-model arm spread against limb/body intersection

Dance clips are authored for the standard mannequin: on chunkier models
the same joint angles drive the arms through the torso (the ninja is
clean because its proportions match). New 'Apertura braccia' slider
(0-35deg, saved per model path): the upper arms get an extra outward
rotation about the world Z axis during clip playback (left +, right -),
solved back into each bone's local frame through the parent rotation.

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

src/visualizer.js

@@ -97,6 +97,7 @@ class Visualizer {
       });
       if (this._clipFilter) this.model3d.clipFilter = this._clipFilter;
       if (this._manualBpm) this.model3d.manualBpm = this._manualBpm;
+      if (this._armSpread) this.model3d.armSpread = this._armSpread;
     }
     if (this._pendingGlb) { this.model3d.setModel(this._pendingGlb); this._pendingGlb = null; }
     return this.model3d;
@@ -130,6 +131,11 @@ class Visualizer {
     if (this.model3d) this.model3d.manualBpm = this._manualBpm;
   }
 
+  setArmSpread(deg) {
+    this._armSpread = (deg || 0)*Math.PI/180;
+    if (this.model3d) this.model3d.armSpread = this._armSpread;
+  }
+
   // Upload a custom source (HTMLImageElement / HTMLCanvasElement) for the
   // SVG/Image effect family. Flipped on the Y axis to match screen space.
   setTexture(source) {