fix: 修复从左侧模式切到混合模式首页不显示在左侧菜单问题

src/layouts/MixLayout.vue

@@ -207,8 +207,15 @@ watch(
   () => route.path,
   (newPath) => {
     const topMenuPath = extractTopMenuPath(newPath);
-    if (topMenuPath !== activeTopMenuPath.value) {
+    const isTopMenuChanged = topMenuPath !== activeTopMenuPath.value;
+
+    if (isTopMenuChanged) {
       appStore.activeTopMenu(topMenuPath);
+    }
+
+    // 切换布局（如左侧 -> 混合）时，activeTopMenuPath 可能已是正确值，
+    // 但 mixLayoutSideMenus 仍为空，需要补一次初始化。
+    if (isTopMenuChanged || permissionStore.mixLayoutSideMenus.length === 0) {
       permissionStore.setMixLayoutSideMenus(topMenuPath);
     }
   },