Pullquote: render the block as an <aside>, not a <blockquote>

[dknauss]

What?

Render the core Pullquote block as an <aside> instead of a <blockquote>, with a block deprecation so existing pull quotes keep validating.

Why?

A block quote belongs to the main text and quotes an external source — which is why <cite> lives inside <blockquote>. A pull quote is the opposite: it is paratextual. It lifts, repeats, or paraphrases a line that is already in the article and sets it apart visually, like a gloss in the margin. It quotes nothing external.

That repetition is the point. Because a pull quote duplicates on-page content, anything consuming the page without the visual styling — a screen reader, a print stylesheet, an RSS-to-Markdown pass — needs to tell it apart and skip it. HTML has the element for exactly this, and the spec names the case:

The element can be used for typographical effects like pull quotes or sidebars … and for other content that is considered separate from the main content of the page. — HTML, The aside element

An <aside> is a landmark (role="complementary") that assistive technology can skip. <blockquote> is not, and it asserts a quotation that a pull quote isn't making.

Refs #11610.

How?

• save.js / edit.js: the inner element changes from <blockquote> to <aside> (the unused blockquote.js constant is removed).
• Attributes are unchanged — value/citation still source from <p>/<cite>, so this is purely an element change.
• deprecated.js: a new v7 deprecation reproduces the previous <blockquote> markup. Existing pull quotes validate against it and migrate forward to <aside> on the next edit — no breakage, no data loss.

The <cite> is kept here. Pull quotes arguably shouldn't carry a citation at all, but removing the field would drop existing users' data; that's a separate, more opinionated change. This PR is the conservative, non-disruptive element fix.

Non-disruptive by design

Old content stored as <figure><blockquote><p/><cite/></blockquote></figure> still validates (via v7) and renders unchanged until it's re-edited, at which point it re-saves as <aside>. The full-content fixture suite passes 376/376, including a new core__pullquote__deprecated-7 fixture and every existing deprecated form migrating forward.

Testing Instructions

1. npm run test:unit -- test/integration/full-content/ → 376 pass.
2. Insert a Pull Quote, view the post; the markup is <figure class="wp-block-pullquote"><aside>…</aside></figure>.
3. Paste an old pull quote (<figure class="wp-block-pullquote"><blockquote><p>…</p><cite>…</cite></blockquote></figure>) into a post — it loads without an "unexpected content" error and migrates to <aside> when edited.

AI disclosure

This pull request was prepared with the assistance of an AI agent (Anthropic's Claude, via Claude Code). A human chose the approach (an element change plus a non-disruptive deprecation), directed the work, and reviewed the result; the fixtures were regenerated and verified locally (376/376). The commit carries a Co-Authored-By trailer to the same effect.

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[dknauss]

Quick note for whoever reviews, so the red CI isn't misread:

• The three failing All legs (Node 24 Linux/Windows, Node 20 Windows) are Type checking = cancelled, not failures — they got caught in a concurrency race between two quick force-pushes. The base All (Node 20 Linux) and lint both pass, and the full-content fixture suite is green (376/376), so the code itself is fine; a re-run of those legs should clear them.
• This needs a [Type] label to satisfy type-related-labels — I don't have permission to add one, so I'll leave that to a maintainer.

Happy to rebase or adjust anything (e.g. revisit the <cite> question, which I deliberately left out of scope to keep this non-disruptive).

_{Posted via an AI agent (Claude Code) on the contributor's behalf, with human review.}

[dknauss]

Correction to my note above: Playwright-2 did surface a real issue, not just the cancellations — the element change broke a selector in collaboration-block-gauntlet.spec.ts that looked for [data-type="core/pullquote"] blockquote p. Updated it to aside p in the latest push (the editor now renders the pull quote as an <aside>).

Note that this same test is independently tracked as a flaky test in #78855 (it intermittently fails on the realtime-sync step), so it may still flake there regardless of this change.

_{Posted via an AI agent (Claude Code) on the contributor's behalf, with human review.}