Cache utility-loaded 3D models

[genson1808]

Fixes #93

/claim #93

Summary

• add normalized model extension detection for URLs with query strings or hashes in load3DModel
• cache in-flight and completed utility-loaded models by URL, ignoring only cachebust_origin
• return cloned model instances with cloned geometry/materials so repeated model usage does not share mutable render state
• add focused tests for extension detection, cache-key normalization, and clone isolation

Test plan

• bun test tests/load-model.test.ts
• bun run format:check src/utils/load-model.ts tests/load-model.test.ts
• bun run build

AI-assisted with Codex; I reviewed the diff and kept the change scoped to the remaining load3DModel utility path.

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Project	Deployment	Actions	Updated (UTC)
3d-viewer	Ready	Preview, Comment	May 15, 2026 2:20pm