Restore Tailwind's native spacing scale

[williamneves]

Problem

The preset currently overwrites Tailwind's default spacing system by mapping the base spacing unit to Mantine's --mantine-spacing-md (1rem). This breaks the expected behavior of Tailwind's utility classes:

• Standard Tailwind: p-1 = 0.25rem, p-2 = 0.5rem, p-3 = 0.75rem
• Current preset: p-1 = 1rem, p-2 = 2rem, p-3 = 3rem

This large jump between spacing increments makes it difficult to create fine-tuned layouts and breaks compatibility with existing Tailwind projects.

Solution

This PR removes the --spacing: var(--mantine-spacing-md) line from all relevant files, restoring Tailwind's native spacing scale with 0.25rem increments while preserving all other Mantine design tokens.

Benefits

• Maintains backward compatibility with standard Tailwind spacing
• Allows for more precise layout control with finer spacing increments
• Reduces friction for teams migrating existing Tailwind projects
• Still provides access to Mantine's named spacing variables when needed

This change ensures the best of both worlds: Mantine's design system with Tailwind's intuitive spacing scale.

[songkeys]

Thank you!