[UI] Improve Accessibility (a11y)

[JoshuaAFerguson]

Improve accessibility for screen readers and keyboard navigation.

Requirements:

• ARIA labels on all interactive elements
• Keyboard navigation for all actions
• Focus management in modals
• Color contrast compliance (WCAG AA)

Acceptance Criteria:

• Screen reader tested
• Keyboard-only navigation works
• Lighthouse accessibility score > 90
• WCAG AA compliant

Files: All UI component files