Moves the doc-hygiene plugin from the standalone cc-plugins repo into
cc-os as plugins/os-doc-hygiene/, following the same pattern as
os-vault and os-orchestration. Also commits the previously-unstaged
ADR-019 (global os-orchestration plugin supersedes per-project
orchestration text), which documents the prior migration but never
made it into a commit.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
b235e99145