Fix 500 error when picking Mauve, Olive, Mist or Taupe as the accent colour

[ashwinuae]

Selecting Mauve, Olive, Mist or Taupe (introduced to Filament's Color::all() via Tailwind v4.2) as the status page accent colour via Manage Theme, currently throws a 500. ThemeData's THEMES and GRAYS (and THEME_PAIRINGS) lists were hardcoded and weren't updated with the new shades, so they showed up as in the Accent dropdown with no definitions to back them. Choosing any of these broke every consumer of ThemeData.

Changes

• Added mauve, olive, mist and taupe to ThemeData::GRAYS, since they seemed like a right fit in the base colour set, and not accents.
• Made the lookups non-fatal, so an already-persisted value can't leave a setup with a permanently broken status page:
  • an unknown accent falls back to the Cachet palette.
  • matchPairing() accepts ?string and falls back to zinc.
  • a null accent_content falls back to the matched pairing.
• Replaced constant("Filament\Support\Colors\Color::{$pairingKey}") in compileCss() with a keyed Color::all() lookup, for the same reason as above; i.e. not to throw an invalid pairing.

Tests

Added 'tests/Unit/Data/ThemeDataTest.php' that steps through every option the accent and accent-content dropdowns actually offer (derived from Color::all() rather than hardcoded) and asserts each one compiles.

[jbrooksuk]

Thanks!