fix(skills): clarify modal focus restoration scope in frontend-a11y

skills/frontend-a11y/SKILL.md

@@ -308,7 +308,9 @@ export function Dropdown({ options, onSelect }: { options: string[]; onSelect: (
 
 Focus must move logically when UI state changes — especially for modals and route transitions.
 
-### Modal Focus Trap
+### Modal Focus Restoration
+
+> This example covers initial focus and restoration. For a full focus trap (Tab/Shift+Tab cycling within the modal), use a library like [`focus-trap-react`](https://github.com/focus-trap/focus-trap-react) which handles edge cases like dynamic content and nested portals.
 
 ```tsx
 export function Modal({ isOpen, onClose, title, children }: { isOpen: boolean; onClose: () => void; title: string; children: React.ReactNode }) {
@@ -317,9 +319,11 @@ export function Modal({ isOpen, onClose, title, children }: { isOpen: boolean; o
 
   useEffect(() => {
     if (isOpen) {
+      // Save currently focused element and move focus into modal
       previousFocusRef.current = document.activeElement as HTMLElement;
       modalRef.current?.focus();
     } else {
+      // Restore focus to the element that opened the modal
       previousFocusRef.current?.focus();
     }
   }, [isOpen]);