Migrate color tokens to OKLCH with fallbacks

Goals

• Move every color token from HSL to OKLCH for perceptual uniformity
• Keep HSL fallbacks for browsers without oklch() support
• No visual regression above a deltaE of 1.5 on existing themes

Token mapping

:root {
   /* before */
   --primary: hsl(243 75% 59%);

   /* after — fallback first, then OKLCH override */
   --primary: hsl(243 75% 59%);
}

@supports (color: oklch(0% 0 0)) {
   :root {
      --primary: oklch(58.5% 0.233 277.1);
   }
}

Migration steps