fix: 修复入住管理白屏、重构首页工作台、拍平教务菜单

- Occupancies: 补齐缺失的 Alert import（渲染时 ReferenceError 导致白屏），
  并为两处 api.get 补泛型消除既有类型错误
- Dashboard: 改为待办优先的工作台（待办异常区 + 核心 KPI + 更多指标折叠 +
  图表按重要性重排），修复 fetchData 无限请求循环（loadedRef），
  重活图表用 IntersectionObserver（callback ref）懒加载
- MainLayout: 将三层嵌套的"教室管理"提升为一级菜单，全站菜单统一为两层

apps/admin/src/layouts/MainLayout.tsx

@@ -77,18 +77,18 @@ const allMenuItems: MenuItemType[] = [
     children: [
       { key: '/schedules', icon: <CalendarOutlined />, label: '排课管理', permission: 'schedule:view' },
       { key: '/teacher-workspace', icon: <LaptopOutlined />, label: '教师工作台', permission: 'class:view' },
-      {
-        key: 'classroom-group',
-        icon: <ReadOutlined />,
-        label: '教室管理',
-        permission: 'classroom:view',
-        children: [
-          { key: '/classroom-schedule', icon: <CalendarOutlined />, label: '排期总览', permission: 'classroom:view' },
-          { key: '/classrooms', icon: <ReadOutlined />, label: '教室列表', permission: 'classroom:view' },
-          { key: '/classroom-rentals', icon: <FileProtectOutlined />, label: '租赁订单', permission: 'rental:view' },
-          { key: '/tenants', icon: <TagsOutlined />, label: '租赁方', permission: 'tenant:view' },
-        ],
-      },
+    ],
+  },
+  {
+    key: 'classroom-group',
+    icon: <ReadOutlined />,
+    label: '教室管理',
+    permission: 'classroom:view',
+    children: [
+      { key: '/classroom-schedule', icon: <CalendarOutlined />, label: '排期总览', permission: 'classroom:view' },
+      { key: '/classrooms', icon: <ReadOutlined />, label: '教室列表', permission: 'classroom:view' },
+      { key: '/classroom-rentals', icon: <FileProtectOutlined />, label: '租赁订单', permission: 'rental:view' },
+      { key: '/tenants', icon: <TagsOutlined />, label: '租赁方', permission: 'tenant:view' },
     ],
   },
   {