refactor: route required field color through recipient CSS var pipeline

- Add --recipient-red HSL var and expose as recipient.red in tailwind config
- required entry delegates to generateStyles('red'), matching the pattern
  used by every other recipient color (hover/active/combobox states, shared
  ring shadow layers)
- Gate recipient ring on !isValidating in FieldRootContainer so the
  validation ring is the sole source of truth when active
- Extend RECIPIENT_DYNAMIC_CLASS safelist via CSS_VAR_RECIPIENT_COLORS

packages/ui/components/field/field.tsx

@@ -138,7 +138,7 @@ export function FieldRootContainer({
         data-readonly={readonly ? 'true' : 'false'}
         className={cn(
           'field--FieldRootContainer field-card-container dark-mode-disabled group relative z-20 flex h-full w-full items-center rounded-[2px] bg-white/90 ring-2 ring-gray-200 transition-all',
-          color?.base,
+          !isValidating && color?.base,
           {
             'px-2': field.type !== FieldType.SIGNATURE && field.type !== FieldType.FREE_SIGNATURE,
             'justify-center': !field.inserted,