Clean up and consolidate old 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 the docs: nothing stale or duplicated remains. Checker passes, no trackers or archives exist, ADRs, lessons and research are all cited, and every doc is reachable from the router within 3 hops. No PR. Memory: none applied.