feat: add skeleton visualization toggle for 3D models (#7857)

## Summary

For better support animation 3d model custon node, such as
https://github.com/jtydhr88/ComfyUI-HY-Motion1, add ability to show/hide
skeleton bones in Load3D nodes for models with skeletal animation. Uses
THREE.SkeletonHelper with root bone detection to properly support both
FBX and GLB model formats.

## Screenshots


https://github.com/user-attachments/assets/df9de4a6-549e-4227-aa00-8859d71f43d1

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7857-feat-add-skeleton-visualization-toggle-for-3D-models-2e06d73d365081a39f49f81f72657a70)
by [Unito](https://www.unito.io)

src/locales/en/main.json

@@ -1642,6 +1642,7 @@
     "loadingModel": "Loading 3D Model...",
     "upDirection": "Up Direction",
     "materialMode": "Material Mode",
+    "showSkeleton": "Show Skeleton",
     "scene": "Scene",
     "model": "Model",
     "camera": "Camera",