Migrate to Next.js

We can gain a lot performance improvement by migrating to Next.js
e.g. we can statically generate pages with revalidate = 1second to regenerate pages in the background etc. I am open to ideas and suggestions.

Target branch of PR: nextjs

Start by auditing the existing React application and the proposed nextjs target branch; the issue does not name specific files or tests. Define the migration scope and performance goals before implementation, including whether static generation with one-second revalidation is appropriate. Done means the application runs on Next.js with agreed performance behavior and validation.

Written by the indexing model from the issue text.