V4 Disable flag to disable @layer when exporting

[heggemsnes]

Using Tailwindcss 4 to generate CSS to be used in another package currently causes some issues if the target use Tailwindcss (v3) as well.

newsletter-plugin/dist/index.css @layer baseis used but no matching@tailwind base directive is present.

It would be nice if the CLI or postcss had an option to compile the CSS without any layers to allow for better compatability.