fix(load3d): dispose THREE.Points GPU resources in clearModel() (#11836)

Fixes #11345

## Summary

`clearModel()` in `SceneModelManager` only traversed and disposed
`THREE.Mesh` instances, leaving `THREE.Points` objects (created by
`handlePLYModeSwitch()` for point-cloud mode) leaking GPU geometry and
material memory on repeated point-cloud loads/clears.

## Changes

- `SceneModelManager.ts`: extend the dispose traversal in `clearModel()`
to also handle `THREE.Points`, mirroring the pattern already used by
`removeAllMainModelsFromScene()`.
- `SceneModelManager.test.ts`: add regression test verifying
`geometry.dispose()` and `material.dispose()` are called for
`THREE.Points` children on `clearModel()`.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-11836-fix-load3d-dispose-THREE-Points-GPU-resources-in-clearModel-3546d73d365081718338e824bc3e737d)
by [Unito](https://www.unito.io)

Author: christian-byrne

src/extensions/core/load3d/SceneModelManager.test.ts

@@ -102,6 +102,16 @@ function createMeshModel(name = 'TestModel'): THREE.Group {
   return group
 }
 
+function createPointsModel(name = 'TestModel'): THREE.Group {
+  const geometry = new THREE.BufferGeometry()
+  const material = new THREE.PointsMaterial({ color: 0xff0000 })
+  const points = new THREE.Points(geometry, material)
+  const group = new THREE.Group()
+  group.name = name
+  group.add(points)
+  return group
+}
+
 describe('SceneModelManager', () => {
   describe('constructor', () => {
     it('initializes default state', () => {
@@ -311,6 +321,20 @@ describe('SceneModelManager', () => {
       expect(geoDispose).toHaveBeenCalled()
       expect(matDispose).toHaveBeenCalled()
     })
+
+    it('disposes points geometry and materials', async () => {
+      const { manager } = createManager()
+      const model = createPointsModel()
+      const points = model.children[0] as THREE.Points
+      const geoDispose = vi.spyOn(points.geometry, 'dispose')
+      const matDispose = vi.spyOn(points.material as THREE.Material, 'dispose')
+
+      await manager.setupModel(model)
+      manager.clearModel()
+
+      expect(geoDispose).toHaveBeenCalled()
+      expect(matDispose).toHaveBeenCalled()
+    })
   })
 
   describe('reset', () => {

src/extensions/core/load3d/SceneModelManager.ts

@@ -328,7 +328,7 @@ export class SceneModelManager implements ModelManagerInterface {
       this.scene.remove(obj)
 
       obj.traverse((child) => {
-        if (child instanceof THREE.Mesh) {
+        if (child instanceof THREE.Mesh || child instanceof THREE.Points) {
           child.geometry?.dispose()
           if (Array.isArray(child.material)) {
             child.material.forEach((material) => material.dispose())