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/extensions/core/load3d/Load3DConfiguration.ts

@@ -156,8 +156,9 @@ class Load3DConfiguration {
 
     return {
       upDirection: 'original',
-      materialMode: 'original'
-    } as ModelConfig
+      materialMode: 'original',
+      showSkeleton: false
+    }
   }
 
   private applySceneConfig(config: SceneConfig, bgImagePath?: string) {

src/extensions/core/load3d/Load3d.ts

@@ -727,6 +727,19 @@ class Load3d {
     return this.animationManager.animationClips.length > 0
   }
 
+  public hasSkeleton(): boolean {
+    return this.modelManager.hasSkeleton()
+  }
+
+  public setShowSkeleton(show: boolean): void {
+    this.modelManager.setShowSkeleton(show)
+    this.forceRender()
+  }
+
+  public getShowSkeleton(): boolean {
+    return this.modelManager.showSkeleton
+  }
+
   public getAnimationTime(): number {
     return this.animationManager.getAnimationTime()
   }

src/extensions/core/load3d/SceneModelManager.ts

@@ -30,6 +30,8 @@ export class SceneModelManager implements ModelManagerInterface {
   originalURL: string | null = null
   appliedTexture: THREE.Texture | null = null
   textureLoader: THREE.TextureLoader
+  skeletonHelper: THREE.SkeletonHelper | null = null
+  showSkeleton: boolean = false
 
   private scene: THREE.Scene
   private renderer: THREE.WebGLRenderer
@@ -414,9 +416,69 @@ export class SceneModelManager implements ModelManagerInterface {
       this.appliedTexture = null
     }
 
+    if (this.skeletonHelper) {
+      this.scene.remove(this.skeletonHelper)
+      this.skeletonHelper.dispose()
+      this.skeletonHelper = null
+    }
+    this.showSkeleton = false
+
     this.originalMaterials = new WeakMap()
   }
 
+  hasSkeleton(): boolean {
+    if (!this.currentModel) return false
+    let found = false
+    this.currentModel.traverse((child) => {
+      if (child instanceof THREE.SkinnedMesh && child.skeleton) {
+        found = true
+      }
+    })
+    return found
+  }
+
+  setShowSkeleton(show: boolean): void {
+    this.showSkeleton = show
+
+    if (show) {
+      if (!this.skeletonHelper && this.currentModel) {
+        let rootBone: THREE.Bone | null = null
+        this.currentModel.traverse((child) => {
+          if (child instanceof THREE.Bone && !rootBone) {
+            if (!(child.parent instanceof THREE.Bone)) {
+              rootBone = child
+            }
+          }
+        })
+
+        if (rootBone) {
+          this.skeletonHelper = new THREE.SkeletonHelper(rootBone)
+          this.scene.add(this.skeletonHelper)
+        } else {
+          let skinnedMesh: THREE.SkinnedMesh | null = null
+          this.currentModel.traverse((child) => {
+            if (child instanceof THREE.SkinnedMesh && !skinnedMesh) {
+              skinnedMesh = child
+            }
+          })
+
+          if (skinnedMesh) {
+            this.skeletonHelper = new THREE.SkeletonHelper(skinnedMesh)
+            this.scene.add(this.skeletonHelper)
+          }
+        }
+      } else if (this.skeletonHelper) {
+        this.skeletonHelper.visible = true
+      }
+    } else {
+      if (this.skeletonHelper) {
+        this.skeletonHelper.visible = false
+      }
+    }
+
+    this.eventManager.emitEvent('skeletonVisibilityChange', show)
+  }
+
   addModelToScene(model: THREE.Object3D): void {
     this.currentModel = model
     model.name = 'MainModel'

src/extensions/core/load3d/interfaces.ts

@@ -34,6 +34,7 @@ export interface SceneConfig {
 export interface ModelConfig {
   upDirection: UpDirection
   materialMode: MaterialMode
+  showSkeleton: boolean
 }
 
 export interface CameraConfig {