Remove unused starter scaffolding: drizzle/D1, basis decoder, dead modules

[PouyanJay]

The repo was scaffolded from the vinext starter and a good deal of that scaffolding is still present but unreferenced. Removing it drops three npm advisories and roughly 600 KB of shipped assets.

Database scaffolding — unused

drizzle is not imported anywhere in app/, and .openai/hosting.json has "d1": null, so no binding is ever created.

• drizzle-kit (devDependency) — pulls the @esbuild-kit/* chain, 3 of the 18 advisories in Security: 18 npm advisories, incl. 10 reaching production via next and react-server-dom-webpack #12
• db/ — schema.ts is explicitly "intentionally empty"
• examples/d1/ — opt-in example surface, never opted into
• drizzle/, drizzle.config.ts, and the db:generate script

Shipped but never loaded

• public/basis/ — ~576 KB. No KTX2Loader is ever registered; loaders.ts sets only the meshopt decoder.
• Keep public/draco/ — also unloaded today, but it is exactly what segmented-asset work would need, and registering DRACOLoader is on the roadmap.

Dead modules

• app/lib/three/tsl-materials.ts — medicalRimNode is never imported
• app/chatgpt-auth.ts — starter SIWC helper, never called
• AnatomyViewer.prefetch() and the AnatomyAssetManager.prefetch() it delegates to — AnatomyApp does its own fetch warm-up on pointer enter, so neither is reachable

Documentation

README.md is still the untouched vinext starter readme — it documents D1 bindings and ChatGPT sign-in, and says nothing about Anatomy Atelier.

Deliberately out of scope

The non-functional nav items (Systems, Library, Notes) and the quiz answer buttons are dead UI, not dead code. Removing visible features is a product decision, not cleanup, so they are left alone here.