Consolidate and clean documentation architecture

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 tree was already single-homed (checker green, ≤3 hops, ADR homes live, no archives). Fixed one stale public privacy line citing an internal task id. Quick gate green; PR #7828 queued. Memory: none applied.