M10 — Docs + diagrams + README

[nficano]

Goal

Docs + diagrams + README.

Scope

• Add docs/ tree per Phase 8
• Add six diagram pairs under docs/diagrams/<name>-{light,dark}.{dot,svg} per Phase 9
• Add make diagrams target + pre-commit hook
• Rewrite README.md per Phase 8 §3
• Replace CONFORMANCE.md stub with the row-by-row matrix mirroring TS, citing arcp/<path>.py:Lline

Spec §

§1–§16 (cited per page)

Risk

L