Build an accessible Accordion component in React.

Requirements:

1. Multiple sections, each with a header and content.
2. Clicking a header toggles its content visibility.
3. More than one section can be open at once.
4. Accessibility:
   • Headers must be button elements.
   • Apply ARIA attributes: aria-expanded, aria-controls, and link panels with aria-labelledby.
   • Panel content should have role="region".
5. Keyboard support:
   • <Enter>/<Space> toggles a section.
   • Up/Down Arrow keys move focus between headers.
6. Focus on accessibility and functionality over styling.