feat: add alpha support for fromTailwind

[APlusTotalgut]

Summary

Extend fromTailwind() to support all Tailwind color-related prefixes and add alpha handling.

Details

• Added support for all Tailwind color prefixes such as bg-, border-, text-, fill-, and stroke-, following the official documentation:
  https://tailwindcss.com/docs/colors#using-color-utilities
• Implemented alpha parsing so classes with / (e.g., bg-green-500/40) are supported — only when followed by a number or when using white or black.
• transparent, current, and inherit now return the lastValidColor instead of producing an invalid color.
• When alpha is below 50%, text color automatically switches to black for better contrast.
• Added luminance-based calculation for more accurate color adaptation and readability.

Impact

Improves the versatility and accuracy of fromTailwind() when parsing color utilities,
enabling proper handling of prefixes and alpha transparency.

[vercel]

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