🩹(frontend) add missing disabled styling for primaryDarkText button

Implement the missing disabled state styling for the
primaryDarkText button variant to ensure consistent UI feedback
when the button is not interactive.

src/frontend/src/primitives/buttonRecipe.ts

@@ -211,6 +211,9 @@ export const buttonRecipe = cva({
           outlineColor: 'focusRing',
           outlineOffset: '2px',
         },
+        '&[data-disabled]': {
+          opacity: 0.2,
+        },
       },
       quaternaryText: {
         backgroundColor: 'transparent',