Clean up and consolidate technical 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 ADR register and living docs (already largely clean: no dangling citations, Home paths resolve). Stripped task-number/quarantine history from 3 files. Quick gate green; PR #6952 queued. Memory: none applied.