Clean 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

Audited docs with context-architecture skill; tree already clean (no stale specs/trackers, ADRs live and consistent, all docs routed). No changes needed, no PR.