Implement Tailwind v4 Support

[endigo9740]

Describe the feature in detail (code, mocks, or screenshots encouraged)

After a lengthly review and audit, we've determined that Skeleton v3's Tailwind plugin will not be supported in Tailwind v4.

• Audit: https://walnut-fly-221.notion.site/Tailwind-v4-Audit-18a66a04713c80078d85c672be0122b0?pvs=74

As such we've opted to delay Skeleton v3's launch until we can rewrite the core features to support the new CSS-based configuration. We've detailed this process in the following two posts:

• Skeleton v3 has been delayed #3175
• Tailwind v4 Support - RFC and Status Update #3192

Goal

This ticket merely represents the overall initiative. This will happen in a three phase process:

• Phase 1: Cleanup and prep for the rewrite
• Phase 2: Port features 1:1 to the new package format
• Phase 3: Implement breaking changes and new features

What type of pull request would this be?

New Feature

Provide relevant links or additional information.

I'll link related bugs and issues that we'll likely sort while porting things forward