fix: use tailwind 4.x bg clases with modifiers

[sohara]

In adopting Ruby UI I noticed that the Table component class names were not being merged correctly, which broke the hover effect.

• bg-opacity utilities are removed in Tailwind 4
• As such recent versions of tailwind_merge no longer supports them:

[8] pry(main)> merger = TailwindMerge::Merger.new
[7] pry(main)> merger.merge("border-b transition-colors hover:bg-muted hover:bg-opacity-50 data-[state=selected]:bg-muted")
=> "border-b transition-colors hover:bg-opacity-50 data-[state=selected]:bg-muted"

For RubyUI, recent versions of Tailwind and tailwind_merge are installed or recommended by default.

I noticed that the docs for RubyUI get around this by using a version of tailwind merge that has tailwind 3.x semantics, but I think it would be best to use Tailwind 4 semantics/utilities.

[stephannv]

LGTM! Thanks!