feat: a Gutenberg design system for core blocks

[ogorzalka]

Why

Unlike Buzz, Apiary had no design system for core blocks: theme.json declared no styles, so the editor showed WordPress's defaults (full width, no type scale), while the front styled content with Tailwind Typography (prose). Editor and page never matched.

What

• theme.json styles every core block from the @theme presets: root, elements (h1–h6, button, caption, cite), and blocks — paragraph, heading, list, quote (amber rule), pullquote, button/outline, separator, table, code, preformatted, verse, details, image, gallery, group, search, post/query/site title. contentSize 45rem (the post column), wideSize 80rem.
• Links are styled inside content blocks (paragraph, list, table, verse), never globally: a global link rule reached WooCommerce's and the templates' own links (a product's category link went from muted to underlined foreground before this was scoped).
• app/Cms/StyleLayers.php (same as theme-default): WordPress's block library and global styles go in cascade layers under Tailwind's utilities — theme, base, wp-core, wp, components, utilities — so theme.json beats the reset and the block library, and a Tailwind class in a template always wins. Independent of where WordPress 7 prints them (the footer of a Blade page).
• Post and page content: prose → is-layout-flow (the block gap, as in the editor). Product descriptions keep prose.
• bin/tests/design-system.php, run in the Contract job: every preset / custom variable the styles use exists (WordPress's 2xl → 2-xl naming), no Tailwind-only variable, no selector list in a block's css.

Checked

On a fresh 13.34.0 site with WooCommerce and the CI shop seed: a kitchen-sink post (every core block), front vs editor, now match. Home, shop, product and account compared with main pixel by pixel: same layout and heights; the remaining differences are default text going from #000 to the palette's foreground, and on My account the form sits 8px higher and "Lost your password?" is no longer underlined — both came from prose leaking into the WooCommerce page, the template's own classes now apply.