docs: shorten public headings and search titles (#39)

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Headings from the docs foundation, SDK/React guides, and hosted workshop
were too long and read like engineer lectures. This rewrites public
chrome only.

**What changed**
- Landing H1 is now `Review DNS, then write`. Document title carries the
DNS provisioning query and the reviewable-plans benefit.
- Workshop document title names the React DNS components. H1 stays
`Workshop`.
- Docs H1s are a few words. `seo.title` is the search title; Blume
appends ` - DomainKit`, and the rendered document titles land in the
50–60 character range with a unique benefit.
- Meta descriptions sit in the 120–160 range on public pages. OG and
JSON-LD follow those titles and descriptions.
- Callout and procedure headings such as continuation storage,
server-side credentials, cleanup, and records-from-parts are shortened.
- Nav labels stay short (`Overview`, `Quickstart`, `Core`,
`Connections`, `Plans`, `Transport`).

Documentation body is unchanged except page leads. No layout or UI
changes.

`blume audit` is clean (0 errors, 0 warnings).

**Not in this PR**
- No merge of the docs stack.
- No product claims beyond what DomainKit actually does: reviewable DNS
plans, digest-bound apply, fail-closed writes, Cloudflare/Vercel
connections, React flows over a host-owned transport.
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Co-authored-by: Cursor Agent <cursoragent@cursor.com>