Add Tailwind v4.2 tinted neutral colours to accent and button

[joshhanley]

The Scenario

Tailwind CSS v4.2 introduced four new tinted neutral colour palettes: mauve, olive, mist, and taupe. These sit alongside the existing neutrals (slate, gray, zinc, neutral, stone) as alternative grey scales with subtle colour undertones.

The Solution

Added mauve, olive, mist, and taupe to the two components that already support the full suite of neutrals (slate, gray, zinc, neutral, stone):

• accent.blade.php
• button/index.blade.php

These use the same neutral pattern as the existing greys.

The following components were excluded because their colour match statements only use zinc as their neutral — they don't support slate, gray, neutral, or stone, so adding the new tinted neutrals would be inconsistent:

• badge/index.blade.php
• callout/index.blade.php
• text.blade.php
• avatar/index.blade.php
• navbar/badge.blade.php
• navlist/badge.blade.php

Fixes #2408