docs(whp): rework DNS page for new Domains & DNS UI

The WHP DNS area was reworked from the old Domains page (left-side add
form + right-side DNS Management dropdown) into a searchable Domains &
DNS list plus a dedicated per-domain DNS records editor.

- Recapture whp-domains.png against the new list layout
- Add screenshots for the Add Domain modal, records editor, inline
  Add Record row, and bulk-action toolbar
- Add capture-dns.ts (fleet-redacted, viewport-only) following the
  existing capture-admin.ts pattern
- Rewrite add-a-domain.mdx Add Domain steps for the modal flow and
  point at the new records editor
- Add manage-dns-records.mdx how-to (add/edit/delete, type filter,
  bulk actions, verification, troubleshooting); renumber sidebar order

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/content/docs/whp/how-to/backups.mdx

@@ -2,7 +2,7 @@
 title: Backups
 description: Run on-demand and scheduled backups of your sites and databases, and confirm they're succeeding.
 sidebar:
-  order: 4
+  order: 5
 ---
 
 import { Steps, Aside } from '@astrojs/starlight/components';