SEO helpers, JSON-LD, and EN/ES hreflang on the marketing site

The marketing site now ships a proper SEO infrastructure: per-page useSeo helpers, structured data in @graph form (Organization, WebSite, BreadcrumbList), and EN/ES hreflang alternates declared correctly on every page.

The result is consistent metadata across the site and rich-snippet eligibility on the home, comparison pages, and product pages. Indexation has been monotonically improving since.