nook: fix the landing title, isolate /blog, grow the sitemap

The landing page spent its strongest on-page signal on the word "Home";
the title now carries the positioning line and the OG title carries the
full brand phrase. /blog on a product subdomain served the personal blog
in dev (vinxi ignores the vercel.json rewrites that protect production),
splitting the brand and crawl equity — subdomain hits now render the
shared 404. /agents, /changelog and /faq join the sitemap registry so
they are indexed as they land.

Tests: bun test (539 pass); vinxi build clean, no new tsc errors.

Issues: FRE-8, FRE-15, FRE-9

src/routes/nook/index.tsx

@@ -55,10 +55,10 @@ export default function NookLanding() {
     <>
       <EdgeCacheHeaders maxAge={300} />
       <PageHead
-        title="Home"
+        title="Agent control for your Mac"
+        ogTitle="The Nook — agent control for your Mac"
         description="The Nook — a native macOS utility for coding-agent orchestration, fan and thermal control."
         ogImage={`https://${site().domain}/nook/og.png`}
-        ogTitle="The Nook — native macOS agent orchestration"
         ogDescription="A one-time-purchase macOS app for coding-agent orchestration, fan control, and thermal insight."
       />