Marketing site: add Open Graph + Twitter Card link-preview metadata and a 1200x630 social share card (public/og-image.png), so sharing routekit.dev renders a branded preview (title, description, image) instead of a bare imageless fallback. og:image uses an absolute URL (relative paths are silently dropped by scrapers). Preview copy adopts the "project operating system" framing; the on-page title/description keep their current framing pending a separate positioning pass.