Builder workbench and renderer update benchmarks

[agustin-littlehat]

Summary

• reuse glTF animation caches and add vanilla polygon leaf update optimizations
• add renderer update/mount benchmark harnesses and rename the chrome trace skill
• overhaul the website builder with shape placement, import, URL scene state, grid controls, and mesh editing

Verification

• pnpm test
• pnpm build
• git diff --check origin/main..HEAD
• browser smoke: /builder renders, Box placement works, scene URL param updates, no console errors