docs(site-builder): add 5-article Site Builder section (Beta)

Adds /whp/site-builder/ with overview, getting-started, blocks-and-pages,
styling, and publishing. Wired as a 'Site Builder' sidebar group with a
Beta badge.

- Captured real screenshots via the demo account through a redaction
  step (server names, domain, demo-user all swapped for placeholders)
- New beta-callout partial shared across all 5 articles
- capture-site-builder.ts is local-only (uses tools/screenshots/.env
  for demo creds, never runs in CI)

src/content/docs/whp/site-builder/publishing.mdx

@@ -0,0 +1,79 @@
+---
+title: Publishing & code injection
+description: Drafts vs. publish, device previews, and adding analytics, custom fonts, or global CSS via the custom head code panel.
+sidebar:
+  order: 5
+---
+
+import { Aside } from '@astrojs/starlight/components';
+import Beta from '~/content/partials/beta-callout.mdx';
+import Support from '~/content/partials/support-link.mdx';
+
+<Beta />
+
+## Drafts vs. publish
+
+Site Builder separates "save my edits" from "make these edits live."
+
+- **Save** stores your edits as a draft on the server. You can close the editor and come back; your work is preserved. The live site doesn't change.
+- **Publish** renders the site, writes the resulting HTML and assets to the site's docroot, and serves it to visitors on the next request.
+
+The two buttons are in the top right of the editor.
+
+<Aside type="tip">
+  Treat **Save** as your "ctrl-S" and **Publish** as your release button. Save liberally; publish when you're ready.
+</Aside>
+
+## Preview before publishing
+
+Two previews are available, both without affecting the live site:
+
+- **Inline preview** — the desktop/tablet/mobile toggle on the top bar swaps the canvas viewport so you can see how the page reflows.
+- **Full-window preview** — click **Preview** at the top to see your draft rendered without the editor chrome. Use this to read the page like a visitor.
+
+If you want to share a preview with someone outside your account, save the draft, then publish to a staging site (a separate WHP site you keep around for review).
+
+## Custom head code
+
+The **Code** button at the top of the editor opens a modal where you can paste content into the `<head>` of every page on the site.
+
+![Custom head code editor](~/assets/screenshots/whp/whp-site-builder-code.png)
+
+Common uses:
+
+- **Google Analytics, Plausible, Fathom, or other analytics** — paste the tracking snippet they give you.
+- **Custom fonts** — `<link>` tags pointing at Google Fonts, Fontsource, or your own hosted font.
+- **Global CSS overrides** — inline `<style>` blocks for tweaks the Styles panel can't reach.
+- **Verification tags** — `<meta>` tags for Google Search Console, Bing Webmaster, etc.
+
+Click **Done** to close the modal. The code is injected on the next publish.
+
+<Aside type="caution">
+  Whatever you paste here runs on every page. Test analytics in your browser's dev tools before publishing widely, and keep any inline `<script>` content small — slow scripts make every page slower.
+</Aside>
+
+## Undo / redo
+
+The two arrows in the top toolbar (left of **Templates**) walk your edit history backwards and forwards. They cover the current editing session — once you close the editor and come back, the undo stack resets.
+
+## Reverting a published version
+
+Site Builder writes a clean copy on each publish, so there's no built-in "rollback" button. If you publish a version you regret:
+
+- Make the corrective edits and publish again — usually the fastest fix.
+- For more serious mistakes, restore from a [WHP backup](/whp/how-to/backups/). The site's domain folder is included in your scheduled site backups.
+
+## Submitting feedback
+
+Site Builder is in beta. The top bar has a **Submit feedback** link — please use it for anything weird, missing, or broken. The team reads every report.
+
+## Related
+
+- [Getting started](/whp/site-builder/getting-started/)
+- [Blocks & pages](/whp/site-builder/blocks-and-pages/)
+- [Styling your site](/whp/site-builder/styling/)
+- [Backups](/whp/how-to/backups/)
+
+## Still stuck?
+
+<Support />