- Replace ImportMeshAsync with LoadAssetContainerAsync for person.stl
- Cache loading promise to prevent race conditions and multiple fetches
- Use instantiateModelsToScene() to create mesh instances from cached container
- Simplify buildMesh signature to use DefaultScene singleton
- Add Havok physics WASM prefetch hint to index.html
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Co-Authored-By: Claude <noreply@anthropic.com>