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

Scrubbed docs/ADRs/specs/trackers/router; already clean, no change needed, so no PR. Memory: none applied.