faelscarpato/capyviewport ? reverse-engineered prompt

Build me a web app where I can paste any website URL and instantly preview how it looks on multiple screen sizes at once, like mobile, tablet, and desktop. I want it to run a site audit too, with Lighthouse scores for performance, accessibility, SEO, and best practices, plus some extra checks that help me spot common layout and metadata issues even if the audit service fails.

Make the interface feel polished and easy to use, with a clear place to enter the URL, a results area, and visual previews that are simple to compare side by side. I also want a social preview section so I can see how the page would look when shared, and a way to inspect heading structure and key page metadata.

If possible, include support for AI powered suggestions and a way to download a small PWA starter kit or generated files for the site. Look up current docs online if you need to.