Dispose temporary STEP conversion resources

[cwklurks]

Summary:

• Dispose the temporary OCCT-generated Three.js group after STEP-to-GLB export completes or fails.
• Free conversion-only geometries and materials immediately instead of retaining them until GC.
• Leave the existing GLB/localStorage/blob cache behavior unchanged.

/claim #93

Checks:

• bun -e 'import * as THREE from "three"; import { disposeStepConversionResources } from "./src/utils/dispose-step-conversion-resources"; const group = new THREE.Group(); const geometry = new THREE.BufferGeometry(); const material = new THREE.MeshStandardMaterial(); let geometryDisposed = 0; let materialDisposed = 0; geometry.dispose = () => { geometryDisposed += 1 }; material.dispose = () => { materialDisposed += 1 }; group.add(new THREE.Mesh(geometry, material)); disposeStepConversionResources(group); if (geometryDisposed !== 1 || materialDisposed !== 1) throw new Error(dispose failed: ${geometryDisposed}/${materialDisposed}); console.log("dispose smoke passed")'
• bunx biome check src/three-components/StepModel.tsx src/utils/dispose-step-conversion-resources.ts

Note: bun run build completed the ESM bundle locally, then stalled in DTS generation for several minutes, so I stopped it.

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Project	Deployment	Actions	Updated (UTC)
3d-viewer	Ready	Preview, Comment	May 23, 2026 5:49pm

[cwklurks]

Follow-up after an adversarial review pass: I added a focused regression test for the owned STEP conversion disposal helper, covering both single-material and material-array meshes. Scope note: this PR is intentionally the narrow STEP conversion resource-cleanup slice, not a global loader/cache rewrite.