Introduce proper v4 support for new apps

[flavorjones]

Main changes to the installer:

• bump the dep on tailwindcss-ruby to ~> 4.0
• drop the config.tailwind.js file, and the -c option from the tailwindcss command
• add import "tailwindcss"; to application.tailwind.css
• update class names in the templates
• remove the Inter font (see below)

Note that this PR also removes the Inter font, which may leave an orphaned stylesheet reference in existing apps that upgrade:

# previously installed into layouts/application.html.erb
<%= stylesheet_link_tag "tailwind", "inter-font", "data-turbo-track": "reload" %>

This will need to be replaced/fixed by an upgrade generator/task, but I don't think it needs to be part of this PR right now.

cc @EricGusmao for feedback

Closes #463

[EricGusmao]

@flavorjones wow, so fast! There is still something missing though, renaming the generator class names to suport the newer ones that were renamed, as my commit fd342bc

for reference: https://tailwindcss.com/docs/upgrade-guide#renamed-utilities

[flavorjones]

Edited this PR to remove the injected compatibility styles. I'll make that part of the upgrade generator in a separate PR.

[flavorjones]

@EricGusmao Thanks for the commit updating class names, I've cherry-picked that into this PR.

[EricGusmao]

Edited this PR to remove the injected compatibility styles. I'll make that part of the upgrade generator in a separate PR.

so the idea is to create a upgrade generator to patch current installations?

[flavorjones]

so the idea is to create a upgrade generator to patch current installations

Yes, I've got one ready to create a PR with that's pretty simple -- does minimal patching and then runs the upstream upgrader.

@EricGusmao Do you agree this PR is OK to merge? Can you think of anything missing for the "tailwindcss:install" use case in a new app?

[flavorjones]

I think this is a good improvement, so I'm going to merge it. We can continue to fix things as we find them.

[EricGusmao]

@EricGusmao Do you agree this PR is OK to merge? Can you think of anything missing for the "tailwindcss:install" use case in a new app?

Yes, lgtm