Revamp Next.js boilerplate (#81945)
## Overview
This PR replaces the existing Next.js boilerplate with a new minimal
design in light and dark themes.
<img width="1512" height="856" alt="light"
src="https://github.com/user-attachments/assets/542f1a8a-3ee1-466d-9446-e7cdb6ecf3b8"
/>
<img width="3024" height="1710" alt="dark"
src="https://github.com/user-attachments/assets/afb89daa-8bcf-4173-9d47-b7fb2fad70bb"
/>
## Testing
1. Run `pnpm build` at root
2. Enter the template directory (e.g. `cd
packages/create-next-app/templates/app/ts`) then install its
dependencies `pnpm i`
3. Run `pnpm next dev packages/create-next-app/templates/app/ts` at root
4. Open [localhost:3000](http://localhost:3000/)
---------
Co-authored-by: graphite-app[bot] <96075541+graphite-app[bot]@users.noreply.github.com>
Co-authored-by: rauno <freiberggg@gmail.com>
Co-authored-by: skullface <skullface@users.noreply.github.com>
