feat(router): mount Landing at / with auth-aware redirect

- / (anonymous) → LandingView
- / (authenticated) → redirects to /dashboard via new meta.redirectIfAuth
- Remove temporary /landing-preview route (Task 2 helper)
- RouteMeta TS augmentation for redirectIfAuth
- LandingView brand link uses router-link (was <a href>, causing SPA reload)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/router/index.ts

@@ -36,15 +36,6 @@ const routes: RouteRecordRaw[] = [
       title: 'Home'
     }
   },
-  {
-    path: '/landing-preview',
-    name: 'LandingPreview',
-    component: () => import('@/views/landing/LandingView.vue'),
-    meta: {
-      requiresAuth: false,
-      title: 'PURO AI'
-    }
-  },
   {
     path: '/login',
     name: 'Login',
@@ -133,7 +124,13 @@ const routes: RouteRecordRaw[] = [
   // ==================== User Routes ====================
   {
     path: '/',
-    redirect: '/home'
+    name: 'Landing',
+    component: () => import('@/views/landing/LandingView.vue'),
+    meta: {
+      requiresAuth: false,
+      title: 'PURO AI — 你的 AI 订阅，已经付过钱了',
+      redirectIfAuth: '/dashboard'
+    }
   },
   {
     path: '/dashboard',
@@ -542,6 +539,13 @@ router.beforeEach((to, _from, next) => {
     authInitialized = true
   }
 
+  // Auth-aware redirect for public pages that should bounce authenticated users elsewhere
+  // (e.g., Landing / at `/` redirects to /dashboard if user is logged in)
+  const redirectIfAuth = to.meta.redirectIfAuth
+  if (redirectIfAuth && authStore.isAuthenticated) {
+    return next(redirectIfAuth)
+  }
+
   // Set page title
   const appStore = useAppStore()
   // For custom pages, use menu item label as document title

frontend/src/router/meta.d.ts

@@ -7,6 +7,12 @@ import 'vue-router'
 
 declare module 'vue-router' {
   interface RouteMeta {
+    /**
+     * If set, authenticated users visiting this route are redirected to this path.
+     * Used for public pages (e.g., Landing `/`) that should bounce logged-in users to the app.
+     */
+    redirectIfAuth?: string
+
     /**
      * Whether this route requires authentication
      * @default true

frontend/src/views/landing/LandingView.vue

@@ -6,10 +6,10 @@
     <!-- NAV -->
     <nav class="nav">
       <div class="container nav-inner">
-        <a href="/" class="brand">
+        <router-link to="/" class="brand">
           <span class="hex">⬢</span>
           <span>PURO AI</span>
-        </a>
+        </router-link>
         <div class="nav-links">
           <a href="#features">产品</a>
           <a href="/docs">文档</a>