Design a marketer-friendly A/B testing control panel for landing pages. Build a React single-page app where users can create campaigns, define URL-based variants (e.g., /promo-A, /promo-B), map each variant to content in a headless CMS (e.g., Strapi), and ensure each visitor consistently sees the same variant via a cookie. From the app, marketers should be able to browse existing Mailchimp templates, duplicate one, edit content for a specific variant, and publish it back to Mailchimp as a new template for email campaigns. Please propose the architecture and implementation plan (key screens, data model, cookie bucketing strategy, and the Mailchimp integration flow—auth, read, edit, create) with performance and caching considerations for high-traffic pages.