Add accessibility and responsive UX hardening

[Lakes41]

Summary

Improve accessibility, keyboard navigation, and responsive behaviour across the member dashboard, admin screens, navigation, and gated states.

Current Behaviour

The UI uses minimal custom components and utility classes. Some controls use native elements without consistent labels, long wallet addresses are shown directly, and navigation layouts may not scale well on small screens.

Expected Behaviour

Core flows should be usable with keyboard navigation, screen readers, small screens, and high-contrast themes.

Suggested Implementation

Audit UI components and pages for labels, focus states, semantic structure, responsive layout, address truncation, and accessible status messaging. Add reusable helpers where needed.

Files or Areas Likely Affected

• components/nav.tsx
• components/wallet/connect-button.tsx
• components/gated.tsx
• components/ui/
• app/dashboard/page.tsx
• app/admin/**/*.tsx
• app/globals.css

Acceptance Criteria

• Interactive controls have accessible names
• Admin forms use labels associated with inputs and selects
• Wallet addresses are truncated visually without losing full value where useful
• Layout remains usable on small screens
• Focus states are visible and keyboard navigation works through primary flows
• Accessibility expectations are documented in the contributing guide

Additional Notes

This issue should not redesign the product. Keep changes scoped to accessibility, layout robustness, and reusable UI improvements.