Clean up and consolidate stale 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 docs with check_context (Tier-1 green, --audit) and scripted checks: no stale/duplicate/dangling docs, all docs within 2 hops of CLAUDE.md. Nothing to delete; no PR. 10 uncited ADRs kept as live. Memory: none applied.