ixartz/Next-js-Boilerplate ? reverse-engineered prompt

Build me a starter web app using Next.js with both the App Router and Page Router, styled with Tailwind CSS and written in TypeScript. It should have a simple sign up and sign in system out of the box, and let me connect to a database like PostgreSQL or MySQL. I want to be able to see an authentication page, a dashboard or landing page once logged in, and the basic pieces in place for localization (multi-language support) even if it’s just a couple placeholder languages. Make sure the codebase is set up for a good developer experience with testing and formatting ready to use. I just want a solid, modern base so I can add my own features later. Look up any setup steps or current docs online if you need to.