[ACCESSIBILITY] Keyboard navigation and color contrast audit

[wi287g]

Make the dashboard usable for people who don't use a mouse or have color vision differences.

Tasks

• Verify all interactive elements (search, filter, map counties) are Tab + Enter/Space navigable
• Check color contrast ratios for status badge text — WCAG AA minimum 4.5:1
• Add aria-label and role where missing (map div, legend, charts canvas elements)
• Test with NVDA or VoiceOver — confirm county summary is announced on selection
• Add a high-contrast/pattern-fill option for colorblind users (replace red/orange with textures or icons)
• Run Lighthouse accessibility audit; target ≥ 90