Storybook + Next.js 15 demo

This repo aims to reproduce the error when building storybook (but not serving it) when using it with the latest version of nextjs, i.e. v15.

How to reproduce the bug

1. Run npm install --force after downloading the repo
2. Run npm run dev and notice how clicking the main button on the page will trigger an alert, based on the response from a Next.js server action
3. Run npm run storybook and notice that storybook will fail

Now, go into Page.action.ts and uncomment a different line so that the reference to next/header's header() is removed. Run npm run storybook and it will work again.