Clean and consolidate documentation repository

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 the docs tree with the context-architecture skill: already compliant (gate green, ADRs current, no stale trackers/specs, all docs within 2 hops of CLAUDE.md, no real duplication). No changes, no PR. Memory: none applied.