DR-063 — Extend UI adoption posture: broad component adoption, but our shadcn/lucide primitives stay the app default; ID-147 owns the first registry install

Status: accepted · S471 (id-147 grounding, refines id-147 RESEARCH §6 cherry-pick framing)

Owner ruling: adopt Extend broadly (all document components/blocks), but keep the in-tree Radix-shadcn components/ui primitives + lucide as the app default. Re-point vendored Extend components lucide (retire Hugeicons) and re-wire any Extend component that surfaces shared chrome to our primitives; self-contained document viewers MAY retain their Coss UI internals.