An architecture diagram inside a model that defines no cards gets one card
per drawn shared element with a description, as the extension does. Test
covers the resolved JSON; formats.md and SKILL.md describe the rule.
Model tasks (validate, list, scaffold, resolve), diagram tasks (validate,
render), the bundled Archify 3.0.1 runtime and yaml parser under
scripts/vendor, references for authoring, formats and folders, and the
online-shop example model.