feat: enhance modal focus trap with JavaScript and ARIA attributes
Implements focus trap function that cycles Tab/Shift+Tab within modal boundaries,
adds ARIA attributes (role, aria-modal, aria-labelledby) for accessibility
compliance, and integrates focus initialization on modal display.
- Focus trap prevents tab escape from modal dialog
- ARIA attributes: role=dialog, aria-modal=true, aria-labelledby linking title
- Backdrop marked aria-hidden=true to exclude from accessibility tree
- Close buttons have aria-label for screen readers
- Focus initialization calls createFocusTrap on modal show
