SEO prerender pipeline + register AI routes and tighten CSP

- Static prerender + sitemap/robots for marketing, blog, and tool pages
  (entry-server, Seo component, prerender/sitemap scripts, NotFoundPage)
- Register aiRoutes and extend CSP for Turnstile + Spaces image hosts

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

apps/web/package.json

@@ -5,7 +5,7 @@
   "type": "module",
   "scripts": {
     "dev": "vite",
-    "build": "tsc -b && vite build",
+    "build": "tsc -b && vite build && npx tsx scripts/prerender.mts && npx tsx scripts/generate-sitemap.mts",
     "preview": "vite preview",
     "typecheck": "tsc -b --noEmit"
   },