Clean up and centralize outdated documentation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 (checker, ADR register/homes/citations, specs, trackers, lessons, history wording, reachability): all clean and live, nothing stale to delete. No PR. Report uploaded.