Migrate tailwindcss to v4, and use it through vite plugin

[egeakman]

The hidden class no longer seems to work along with other classes that affect display.

I had to use a workaround like this:

${className.includes("hidden") ? "hidden" : "inline-block"}

Also, there seems to be a new preferred way of configuration: inline configuration in CSS. I like it.

I had to tweak some components and pages to make this work, but I most likely missed something somewhere.

Closes #1038

[europython-society]

Preview available

Key	Value
url	https://migrate-tailwind.ep-preview.click
last update	2025-03-11T05:55:30.427Z

[egeakman]

@hypha This will likely create conflicts with the sponsor PR because the colors were defined in the tailwind config. How would you like to move forward with this 🤗

[egeakman]

Let's hold this until the sponsor PR gets merged!

[egeakman]

It is probably the safest option to hold this until after the conference, since it might affect existing and new pages.