Convert 7 UI primitive class components to functional

[rzueger]

Summary

• Convert Button, Dropdown, SingleSelect, IncrementationField, LabeledComponent, ClipboardCopier, and QrCodeGenerator from class components to functional components with hooks
• Replace PropTypes with TypeScript interfaces and default parameters
• Use render-time sync pattern (not useEffect) for prop-to-state synchronization in Dropdown and SingleSelect, preserving the original componentWillReceiveProps/componentDidUpdate timing to avoid visual flash
• Use useRef for Dropdown's async onBlur callback to prevent stale closure in requestAnimationFrame
• Replace withTranslation() HOC with useTranslation() hook in QrCodeGenerator

Test plan

• npm test — 1746 tests pass
• npm run typecheck — clean
• Reviewed for stale closure issues in async handlers (rAF, timeouts)
• Reviewed prop-to-state sync timing matches original lifecycle methods
• Cypress E2E — Button, Dropdown, SingleSelect, IncrementationField are exercised by departure/arrival wizard specs