fix(ui): 메뉴 클릭 네비게이션 + 드롭다운 딜레이 추가

frontend/src/components/layout/Header.jsx

@@ -60,6 +60,7 @@ export default function Header() {
   const [activeMenu,  setActiveMenu]  = useState(null);
   const [mobileOpen,  setMobileOpen]  = useState(false);
   const [member,      setMember]      = useState(null);
+  const closeTimer = React.useRef(null);
   const location = useLocation();
   const navigate = useNavigate();
 
@@ -117,10 +118,11 @@ export default function Header() {
             {MENU.map(menu => (
               <div key={menu.id}
                    className={`nav-item ${isActive(menu) ? 'active' : ''}`}
-                   onMouseEnter={() => setActiveMenu(menu.id)}
-                   onMouseLeave={() => setActiveMenu(null)}>
+                   onMouseEnter={() => { clearTimeout(closeTimer.current); setActiveMenu(menu.id); }}
+                   onMouseLeave={() => { closeTimer.current = setTimeout(() => setActiveMenu(null), 200); }}>
                 <button className="nav-trigger" aria-haspopup="true"
-                        aria-expanded={activeMenu === menu.id}>
+                        aria-expanded={activeMenu === menu.id}
+                        onClick={() => navigate(menu.children[0].path)}>
                   {menu.label}
                 </button>
                 {activeMenu === menu.id && (