Clean 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

Docs audit found the tree largely clean; fixed confirmed dead refs, history/date narration and duplicates (PR #6996, queued to merge lane). Quick gate and context check green. Deferred: lessons-learned trims, nginx/requirements comments. Memory: none applied.