maintain-design-system-page

How to build and keep current the /design-system page (the in-site component catalog) and its sibling /brand-kit page on any Astro Knots site — the replacement for Storybook. Use when a site has no /design-system page yet; whenever a component is created, changed, given a variant, or extracted from a spike; when refactoring a spike into components; when knot-check reports uncatalogued components; or when the user mentions "design system page", "component catalog", "brand kit", or "Storybook". Encodes the two pages' scopes, the required entry for each component, the theme and mode contract, noindex, the same-change rule, and how to catch up a catalog that has drifted.