Agent Skills: accessibility-contrast-audit

[Design System] Quantitative accessibility audit for UI - contrast ratios, font sizes, tap targets, heading hierarchy. Use when (1) checking WCAG color contrast compliance, (2) auditing text sizes for readability, (3) validating touch/click target sizes, (4) reviewing heading structure and landmarks, (5) user asks to 'check accessibility', 'audit contrast', 'WCAG compliance', or 'a11y check'.