feat(web): full SEO stack — metadata, JSON-LD, sitemap, robots, OG image

Ported and adapted from the BuildMyDiscord SEO setup:

- lib/seo.ts — single source for site constants, the FAQ data (shared by
  the rendered FAQ and the FAQPage schema so they never drift) and JSON-LD
  builders.
- Rich root metadata: title template, keywords, Open Graph, Twitter card,
  robots directives, canonical.
- JSON-LD: Organization + WebSite + SoftwareApplication sitewide, FAQPage
  on the landing page. No AggregateRating — there are no real reviews yet.
- app/robots.ts — allow all, explicit allow-list for AI answer-engine
  crawlers (GPTBot, ClaudeBot, PerplexityBot, …), disallow private routes.
- app/sitemap.ts — every public marketing + docs route.
- app/opengraph-image.tsx — monochrome on-brand 1200x630 share card.
- app/manifest.ts + public/llms.txt.
- Per-page metadata for pricing, changelog, security, privacy, terms,
  docs, templates and status.
- opengraph-image + apple-icon pinned to the edge runtime — next/og
  crashes during a Node-runtime prerender.

Verified: next build passes; /robots.txt, /sitemap.xml,
/manifest.webmanifest and /opengraph-image all generate.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/components/json-ld.tsx

@@ -0,0 +1,13 @@
+// Renders a JSON-LD structured-data script. The `<` escape prevents a
+// `</script>` sequence in the data from breaking out of the tag.
+export function JsonLd({ data }: { data: object }) {
+  return (
+    <script
+      type="application/ld+json"
+      // biome-ignore lint/security/noDangerouslySetInnerHtml: JSON-LD must be injected as a raw script.
+      dangerouslySetInnerHTML={{
+        __html: JSON.stringify(data).replace(/</g, '\\u003c'),
+      }}
+    />
+  );
+}