feat(style): 超级菜单展开期间 header 保持不透明，关闭后才恢复透明（含防抖期）

src/layouts/SiteLayout.vue

@@ -4,11 +4,12 @@
     <header
       id="header"
       class="fixed top-0 left-0 right-0 z-50 transition-all duration-300 ease-in-out bg-white shadow-sm border-b border-gray-100 dark:bg-gray-900 dark:border-gray-800"
-      :class="
+      :class="[
         navTheme === 'light'
           ? '!bg-transparent !shadow-none !border-transparent hover:!bg-white hover:!shadow-sm hover:!border-gray-100'
-          : ''
-      "
+          : '',
+        { 'menu-open': navTheme === 'light' && activeMega !== null },
+      ]"
       :data-nav-theme="navTheme"
     >
       <div class="flex items-center justify-between h-16 px-6">
@@ -505,4 +506,13 @@ watch(
 #header[data-nav-theme='light']:hover::before {
   opacity: 1;
 }
+/* 超级菜单展开期间：header 保持正常背景（不透明），菜单关闭后恢复透明 */
+#header[data-nav-theme='light'].menu-open {
+  background-color: #ffffff !important;
+  box-shadow: 0 1px 2px 0 rgb(0 0 0 / 0.05) !important;
+  border-bottom-color: rgb(229 231 235) !important;
+}
+#header[data-nav-theme='light'].menu-open::before {
+  opacity: 1;
+}
 </style>