Documentation cleanup and centralization via CLAUDE.md

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: tree already clean (checker green, all docs ≤2 hops from router). Fixed stale TASK_LIST_MAX name, a "new" marker, and ADR provenance prose. Quick gate green; PR #7740 queued to merge lane. Deeper ADR/tag trimming deferred.