feat(landing): LandingView scaffold with Nav + Hero

Temporary route /landing-preview added for dev iteration. Will flip /
to this view once all 6 sections are in place (Task 6).

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

frontend/src/router/index.ts

@@ -36,6 +36,15 @@ 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',