Clean up 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

Audited docs: tree already clean (no trackers, no dead ADR refs, all docs routed). Trimmed ADR-0135 to current truth. Quick gate green; PR #6911 queued to merge lane. No further deletions justified.