Scrub Stale Documentation 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 scrub: audited all docs/ADRs (already near-clean, none stale to delete); routed agent/rule files and provider research from CLAUDE.md, removed provenance tags. Full gate green; PR #5613 merged. Deferred: legacy-name aliases removal.