Adopt OKF docs knowledge base

[yvette-carlisle]

Summary

• migrate docs/ to a Markdown-only OKF + LLM Wiki knowledge base
• add Decodex docs skill family for docs, OKF, wiki routing, and drift audits
• split research references, retire checked-in research JSON logs, and wire docs-impact completion gates

Validation

• cargo make check
• cargo test -p decodex plugin_surface -- --nocapture
• cargo run -p decodex --bin decodex -- docs lint
• plugin-eval: plugins/decodex 100/A/low; docs skills 100/A/low