Improve keyboard navigation and accessibility states

[imperator-clawdius]

The app should be more comfortable for keyboard users and screen-reader users.\n\nSuggested scope:\n- Check tab order through the offer builder, tabs, cards, and lead form.\n- Add visible focus states where needed.\n- Add labels or aria text where controls are unclear.\n- Confirm color contrast for badges and buttons.\n\nVerification:\n- npm test\n- Manual keyboard pass from top to bottom\n- Optional Lighthouse accessibility check