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/app/manifest.ts

@@ -0,0 +1,15 @@
+import { SITE_DESCRIPTION, SITE_NAME } from '@/lib/seo';
+import type { MetadataRoute } from 'next';
+
+export default function manifest(): MetadataRoute.Manifest {
+  return {
+    name: SITE_NAME,
+    short_name: 'BuildMyMCP',
+    description: SITE_DESCRIPTION,
+    start_url: '/',
+    display: 'standalone',
+    background_color: '#0a0a0b',
+    theme_color: '#0a0a0b',
+    icons: [{ src: '/icon.svg', sizes: 'any', type: 'image/svg+xml' }],
+  };
+}