Clean up and consolidate stale documentation

Use context architecture skill to scrub all old documentation, including instructions, specs, trackers, ADRs - delete everything superseeded and stale, remove references to historical decisions, delete duplicates, single home everything and make sure all documentation is accessible from CLAUDE.md router in a few steps

Docs audit found nothing stale: checker green, no trackers/active specs, all docs within 3 hops of CLAUDE.md, ADR homes all resolve. No change, no PR. Memory: none applied.