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

Docs already near-clean; audited ADRs/policies/specs/lessons, trimmed duplicate ADR sentences, reordered ADR-0173, dropped dated note. Quick gate green; PR #7935 queued. Larger ADR merges deferred (named in report). Memory: none applied.