Accessibility audit: ARIA, keyboard navigation, screen reader

[cd-rite]

Summary

Comprehensive accessibility audit and remediation across the new client.

Split from #1925.

Work Items

• ARIA roles and labels on all interactive elements
• Keyboard navigation — tab order, focus management, keyboard shortcuts
• Screen reader compatibility — announcements, live regions
• Color contrast verification
• Focus trap management in modals and popovers

Reference

• PrimeVue accessibility: https://primevue.org/accessibility/