feat(#184): change radio-button color variable, fix parity

[anneke]

Summary

• change the "dot" color (the marker) in the input element to fix contrast in Surf Green theme
• make sure Angular component and React component look the same in different themes

Related issue

Closes #184

Type of change

• Fix
• New feature / variant
• Breaking change
• Docs / repo tooling (no package code changed)
• Chore / refactor

Checklist

• pnpm build, pnpm lint, and pnpm format pass
• Storybook story added/updated to cover the change (variants, sizes, states)
• Visual snapshots updated (pnpm test:visual:update after pnpm build-storybook) if appearance changed
• Changeset added (pnpm changeset) — required for any change to @surfnet/curve-react or @surfnet/curve-angular; N/A for docs/CI-only changes
• React and Angular kept in parity, if applicable (contract updated in @surfnet/curve-contracts)

Screenshots

The line around the input given to us by --input does not have high enough contrast with a white background, this needs to be a darker color, see https://www.w3.org/WAI/WCAG21/Understanding/non-text-contrast.html.

[anneke]

To do before merge:

• update input border color if possible
• make changeset (patch)
• update visual baseline

[github-actions]

♿ Accessibility audit — WCAG 2.2 AA

✅ No violations across 362 stories / 10136 theme·mode combinations in @surfnet/curve-angular, @surfnet/curve-react.

Automated axe covers ~30–50% of WCAG 2.2 AA. Keyboard, screen-reader and reflow checks still need a manual pass. Full per-story JSON is in the run’s a11y-reports artifact.