fix(website): SEO canonicals, host redirects, sitemap, app noindex

Addresses the high-volume issues from the Ahrefs audit:
- Worker entrypoint 301s every request not on https://paseo.sh
  (www subdomain and http variants), killing the duplicate-page
  errors and the HTTP→HTTPS internal-link notices.
- pageMeta() emits <link rel="canonical"> and og:url per route;
  every head() call now passes its canonical path.
- /blog stops rewriting itself to /blog?drafts=false; the search
  param only appears when explicitly true.
- Sitemap includes /blog and each post.
- Trim homepage title under SERP truncation, rewrite /agents meta
  description under 160 chars, pad short descriptions on
  /privacy, /download, /cloud, /changelog, /docs.
- app.paseo.sh gets <meta robots=noindex,nofollow> and a
  Disallow-all robots.txt so the SPA shell stops polluting the
  crawl with H1-missing / no-OG / low-word-count warnings.

packages/app/public/index.html

@@ -3,6 +3,7 @@
   <head>
     <meta charset="utf-8" />
     <meta http-equiv="X-UA-Compatible" content="IE=edge" />
+    <meta name="robots" content="noindex,nofollow" />
     <meta
       name="viewport"
       content="width=device-width, initial-scale=1, shrink-to-fit=no, viewport-fit=cover"

packages/app/public/robots.txt

@@ -0,0 +1,2 @@
+User-agent: *
+Disallow: /