Rescue: migrate slow WordPress marketing site to Next.js

Our WordPress marketing site takes 9 seconds to load and got flagged in a security scan. ~40 pages, blog with 300 posts, contact forms, nothing exotic. Migrate to Next.js with a headless setup (or just markdown — convince me), keep SEO intact with proper redirects, and get us under 2s LCP. Content team needs an editor they'll actually use. A previous freelancer started and vanished — there's a half-finished repo to salvage or abandon.