Clean up and consolidate obsolete 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 the docs, ADR register, specs, lessons and router. The tree already conforms, with nothing stale, orphaned or duplicated, so no change and no PR. Run telemetry (trace_summary) was not captured.