Clean up and consolidate old 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

Audit found docs already clean (routed, cited, no stale trackers/specs; advisories were false positives). Only change: removed Task-1931 history from pre-push hook header. Quick gate green; PR 7840 queued. Memory: none applied.