fix: 顶部导航切换后内容区空白

<transition mode="out-in"> 包裹 router-view 时，首次导航后新视图
无法挂载（概览页首次加载正常、切换后所有页面含返回首页均空白，
且无 JS 报错）。改为默认过渡模式 + :key="route.path" 强制按路由
重挂载 + appear 首屏动画；路由改为同步导入简化实现。dev 与生产
构建均验证通过。

frontend/src/App.vue

@@ -35,8 +35,8 @@ onMounted(() => {
   </div>
 
   <router-view v-slot="{ Component }">
-    <transition name="fade-slide" mode="out-in">
+    <transition name="fade-slide" appear>
-      <component :is="Component" />
+      <component :is="Component" :key="route.path" />
     </transition>
   </router-view>
 

frontend/src/router/index.js

@@ -1,12 +1,19 @@
 import { createRouter, createWebHistory } from 'vue-router'
+// 小面板仅 6 个页面，直接同步导入（无需代码分割）
+import LoginView from '../views/LoginView.vue'
+import OverviewView from '../views/OverviewView.vue'
+import SearchView from '../views/SearchView.vue'
+import ThresholdsView from '../views/ThresholdsView.vue'
+import IgnoredView from '../views/IgnoredView.vue'
+import LogsView from '../views/LogsView.vue'
 
 const routes = [
-  { path: '/login', name: 'login', component: () => import('../views/LoginView.vue'), meta: { public: true } },
+  { path: '/login', name: 'login', component: LoginView, meta: { public: true } },
-  { path: '/', name: 'overview', component: () => import('../views/OverviewView.vue') },
+  { path: '/', name: 'overview', component: OverviewView },
-  { path: '/search', name: 'search', component: () => import('../views/SearchView.vue') },
+  { path: '/search', name: 'search', component: SearchView },
-  { path: '/thresholds', name: 'thresholds', component: () => import('../views/ThresholdsView.vue') },
+  { path: '/thresholds', name: 'thresholds', component: ThresholdsView },
-  { path: '/ignored', name: 'ignored', component: () => import('../views/IgnoredView.vue') },
+  { path: '/ignored', name: 'ignored', component: IgnoredView },
-  { path: '/logs', name: 'logs', component: () => import('../views/LogsView.vue') },
+  { path: '/logs', name: 'logs', component: LogsView },
   { path: '/:pathMatch(.*)*', redirect: '/' },
 ]