Support the new Tailwind v4 CSS config

[TheOnlyTails]

Prerequisites

• This feature already exists in shadcn/ui - if not, it won't be considered here so don't continue with your issue.

Describe the feature

Detect when the tailwindcss v4 beta is installed, and generate the config directly into app.css.
I've made an example of such config (that I use in my own app) here: https://gist.github.com/TheOnlyTails/2be83c37d96ed988c8d3353ec8574a75

This new config uses tailwind's new --color-* variables, plus the light-dark() function to handle theming and @utility to extend the container class.

[luxus]

only update to beta and the app.css?

[huntabyte]

When it is stable and ready - duplicate of #1527