Mostly fix TailwindCSS v4 Build issues

[hudsonm62]

Hey Nuno - I've been having a hack at this, however there are 2 problems I don't seem to be able to resolve myself. Hope this PR might help you complete the v4 migration.

• Mostly fixes After updating to v2.83.0, which includes the tailwindcss bump to v4, building the theme CSS from source fails #1985 after the final 2 issues are resolved, and some more testing.

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Seems the old CLi is entirely incompatible with v4, now being a separate package and all. After resolving the CLi package problem, several issues sprung up (in order, as previous is resolved):

• Error: Can't resolve 'components/zen-mode.css' in 'H:\Git\blowfish\assets\css'
  • Resolved by replacing @import 'components/zen-mode.css'; to @import './components/zen-mode.css';
• Error: Cannot apply unknown utility class: rtl:pr-4 + Various others
  • Resolved by updating the tailwind globals in main.css to only @import "tailwindcss";
  • https://tailwindcss.com/docs/installation/tailwind-cli
• Error: Cannot apply unknown utility class: bg-primary-100 + all other overrides
  • Due to the fact tailwind.config.js is no longer used.
  • Can be fixed easily with @config "../../tailwind.config.js";

Now this seems to actually work for the most part, only 2 issues I've been able to spot on the example site is 1. the homepage background layout:

And 2. breadcrumbs:

I couldn't really progress much from here, so I tried the @tailwindcss/upgrade tool. It does make ALOT more changes for a "full" migration, but produces the EXACT SAME result as the above.

This does raise a new concern when/if deprecated classes are removed, but one thing at a time, right?

edit - fix grammar