Add mkdocs.yml (Material theme + nav), docs/index.md, and the first ADR
(docs/architecture/adr-0001-loose-coupling.md, Nygard template) recording
the loose-coupling stance from CLAUDE.md §8. Rewrite the README quickstart
to be accurate and reach a green local environment in under 10 minutes
(correct clone URL, .NET 10 + container-engine prereqs, `make ci` and the
compose smoke), and document building the docs site. Ignore .venv/ and site/.
Verified: `mkdocs build` succeeds; `make lint/build/unit` green.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
