fix(seo): put the brand first in the landing title, scope the docs title

[sardorml]

Searching the brand term now returns the docs homepage above the landing
page. Nothing is broken — the landing is still index, follow with a valid
canonical and nothing in robots.txt blocks it. The two pages simply compete for
the query, and docs wins it.

	<title>	<h1>
docs home	What is CaptureFlow? | CaptureFlow	What is CaptureFlow?
landing	Open-source screen recorder with shareable links — CaptureFlow	Open-source screen recorder with shareable links

Docs names the brand twice in its title and its h1 is the query as a question.
The landing trails the brand at the end of a feature-led title, and its h1 does
not contain the brand at all. For a bare brand query docs is the better on-page
match, so it took the slot — and it is the page that cannot convert anyone.

Changes

• Landing title leads with the brand: CaptureFlow — Open-source screen recorder with shareable links. SITE_TITLE also feeds og:title and
  twitter:title, so all three move together.
• Docs site title becomes CaptureFlow Docs, so pages read
  What is CaptureFlow? | CaptureFlow Docs and stop competing for the bare
  term. This also matches the og:title the docs already published.

themeConfig.siteTitle is deliberately untouched, so the visible nav wordmark
still reads "CaptureFlow" — only the tab and the SERP change. Verified in a
real build: nav renders CaptureFlow, and the only occurrence of "CaptureFlow
Docs" outside <head> is inside VitePress's inlined __VP_SITE_DATA__ script
payload.

Not in this PR

The landing h1 has no brand in it. That is the largest remaining on-page
gap for a brand query, but it is visible hero copy rather than a metadata fix,
so it is a decision for the author, not something to slip into an SEO change.

Verification

• landing renders <title> and og:title brand-first
• docs home builds to What is CaptureFlow? | CaptureFlow Docs; a sub-page to
  Self-hosting overview | CaptureFlow Docs
• pnpm typecheck green, 37/37 web tests pass, docs build clean

Expectations

This will not flip overnight. Titles are re-read on the next crawl, and the
apex was last crawled Aug 10. Worth requesting indexing for / after deploy.

Also worth being honest about ceiling: the AI Overview for this query now
describes CaptureFlow as "a name shared by a few different software tools…
most notably an AI-powered content distribution platform." Google's entity
model still treats .ai as the primary CaptureFlow, and no title change moves
that — only backlinks will.