feat(ui): improve avatar dropdown keyboard accessibility

- Add keyboard event handler for Enter and Space keys
- Support proper dropdown toggle via keyboard navigation
- Prevent default behavior for key events
- Enhance accessibility for screen reader users

components/auth/AvatarDropdown.tsx

@@ -38,6 +38,12 @@ const AvatarDropdown: React.FC<AvatarDropdownProps> = ({
     <div className='relative' ref={dropdownRef}>
       <button
         onClick={() => setIsOpen(!isOpen)}
+        onKeyDown={event => {
+          if (event.key === 'Enter' || event.key === ' ') {
+            event.preventDefault();
+            setIsOpen(prev => !prev);
+          }
+        }}
         className='w-10 h-10 rounded-full bg-slate-200 dark:bg-slate-700 flex items-center justify-center text-lg font-bold text-slate-600 dark:text-slate-300 focus:outline-none focus:ring-2 focus:ring-offset-2 focus:ring-indigo-500 dark:focus:ring-offset-slate-900'
         aria-label='User menu'
       >