✨ Redirect existing users with generations to previews

Update sign-in flow to redirect users with existing generations to the previews index instead of the new preview path. :lipstick: Update navigation links with active states Enhance the header navigation by adding active states for Creations, Features, Pricing, and About links based on the current controller and action. :sparkles: Add sitemap feature with XML response Implement sitemap route and controller to serve XML for SEO. Include static and dynamic theme pages in the sitemap. :recycle: Refactor code structure for better maintainability Organize and streamline code components to enhance readability and ease of future modifications.