Feat(#144): make form fields required

[anneke]

Summary

• make form fields required, and optional only by exception
• adds choice-card variant to radiogroup story
• updates variable used for the border in choice-card surrounding the field

Related issue

#144

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

[github-actions]

♿ Accessibility audit — WCAG 2.2 AA

✅ No violations across 370 stories / 11840 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.

[anneke]

Ik wil deze graag mergen na overleg met het designteam op dinsdag 13 oktober