[codex] Dashboard: Move Howdy greeting into welcome widget

[scruffian]

What?

Moves the personal "Howdy" greeting out of the experimental Dashboard page title and into the bundled Welcome widget as the widget's visible h2 heading.

Why?

The Dashboard page h1 should identify the page topic. A personal greeting works better inside the Welcome widget, where it can label that widget section while preserving the page-level heading as "Dashboard".

How?

• Adds a hasOwnHeading widget metadata flag so a full-bleed widget can provide the heading that labels its widget region.
• Passes the widget chrome titleId through render props for widgets that opt into owning their heading.
• Updates the Welcome widget banner to render Howdy, {display name} as an h2 inside an hgroup, with the previous welcome/version copy as paragraphs.
• Adds regression coverage for a full-bleed widget whose visible h2 labels its region.

Fixes #79240.

Testing Instructions

• npm run test:unit packages/widget-dashboard/src/test/widget-dashboard.test.tsx -- --runInBand
• npm run lint:js -- packages/widget-primitives/src/types.ts packages/widget-primitives/src/components/widget-render/widget-render.tsx packages/widget-dashboard/src/components/widget-frame/widget-frame.tsx packages/widget-dashboard/src/components/widget-render/widget-render.tsx packages/widget-dashboard/src/test/widget-dashboard.test.tsx widgets/welcome/components/banner/banner.tsx widgets/welcome/render.tsx widgets/welcome/widget.ts
• npm run lint:css -- widgets/welcome/components/banner/banner.module.css
• npm run lint:lockfile
• npm run lint:deps
• npm run lint:pkg-json
• npm run build -- --webpack-no-externals --webpack-copy-php --webpack-bundle-analyzer=false --packages=widget-dashboard,widget-primitives

Browser testing was not completed in this workspace because wp-env start cannot connect to Docker (Cannot connect to the Docker daemon at unix:///Users/ben/.docker/run/docker.sock).

[github-actions]

Size Change: 0 B

Total Size: 7.61 MB

_{compressed-size-action}

[github-actions]

Flaky tests detected in 6b559b7.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/28453328013
📝 Reported issues:

• [Flaky Test] supports editable inner blocks within static HTML #79654 in /test/e2e/specs/editor/blocks/html.spec.js