feat(S4): new user onboarding wizard with 3-step guided flow

- Backend: check-login API returns is_new_user flag (no prompt history)
- Vue: OnboardingWizard component (scene select → tips → ready)
- Vue: HomeView conditionally shows wizard for new users
- Auth store: expose isNewUser state, auto-detect on refresh

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

vue-app/src/views/HomeView.vue

@@ -1,48 +1,62 @@
 <script setup lang="ts">
+import { ref, onMounted } from 'vue'
 import { useAuthStore } from '@/stores/auth'
+import OnboardingWizard from '@/components/onboarding/OnboardingWizard.vue'
 
 const auth = useAuthStore()
+const showOnboarding = ref(false)
 const flaskOrigin = import.meta.env.VITE_FLASK_ORIGIN || ''
 const generateUrl = flaskOrigin ? `${flaskOrigin}/` : '/'
 
+onMounted(async () => {
+  if (!auth.ready) await auth.refresh()
+  showOnboarding.value = (auth as any).isNewUser ?? false
+})
+
 function openLegacyGenerate() {
   window.location.href = generateUrl
 }
+
+function onOnboardingDone() {
+  showOnboarding.value = false
+}
 </script>
 
 <template>
   <div class="home">
-    <el-card shadow="never" class="hero">
-      <h1>Vue 3 前端试验田</h1>
-      <p class="lead">
-        与现有 Flask 后端并行开发：开发时 Vite 将 <code>/api</code>、<code>/poetry</code>、<code>/static</code> 代理到后端；会话使用 Cookie（
-        <code>withCredentials</code>
-        ）。建议开发使用 <strong>127.0.0.1:3000</strong>。经典版生成页也可从顶部 <strong>更多</strong> 菜单进入。
-      </p>
-      <el-space wrap>
-        <el-button type="primary" @click="$router.push({ name: 'generate' })">Vue 提示词生成</el-button>
-        <el-button @click="$router.push({ name: 'optimization' })">提示词优化</el-button>
-        <el-button @click="$router.push({ name: 'resume-optimization' })">简历 / 求职信</el-button>
-        <el-button @click="openLegacyGenerate">经典生成页（Flask）</el-button>
-        <el-button @click="$router.push({ name: 'favorites' })">收藏列表</el-button>
-        <el-button @click="$router.push({ name: 'history' })">优化历史</el-button>
-        <el-button @click="$router.push({ name: 'meal-planning' })">饭菜规划</el-button>
-        <el-button @click="$router.push({ name: 'poetry' })">古诗词</el-button>
-        <el-button @click="$router.push({ name: 'android-tools' })">Android 工具</el-button>
-        <el-button @click="$router.push({ name: 'profile' })">个人资料</el-button>
-      </el-space>
-    </el-card>
+    <!-- 新用户引导 -->
+    <OnboardingWizard v-if="showOnboarding" @done="onOnboardingDone" />
 
-    <el-card shadow="never" class="status">
-      <template #header>会话状态</template>
-      <p v-if="!auth.ready">正在检测登录状态…</p>
-      <template v-else>
-        <p v-if="auth.loggedIn">
-          已登录：<strong>{{ auth.nickname || auth.userId }}</strong>
+    <div v-else>
+      <el-card shadow="never" class="hero">
+        <h1>提示词大师</h1>
+        <p class="lead">
+          智能 AI 提示词生成平台：将简单想法变为专业 Prompt，覆盖饭菜规划、古诗词解析、简历优化等 15 种场景。
         </p>
-        <p v-else>未登录（收藏接口仍可能按访客策略返回数据，取决于后端）。</p>
-      </template>
-    </el-card>
+        <el-space wrap>
+          <el-button type="primary" @click="$router.push({ name: 'generate' })">提示词生成</el-button>
+          <el-button @click="$router.push({ name: 'optimization' })">提示词优化</el-button>
+          <el-button @click="$router.push({ name: 'resume-optimization' })">简历优化</el-button>
+          <el-button @click="$router.push({ name: 'meal-planning' })">饭菜规划</el-button>
+          <el-button @click="$router.push({ name: 'poetry' })">古诗词</el-button>
+          <el-button @click="$router.push({ name: 'android-tools' })">Android 工具</el-button>
+          <el-button @click="$router.push({ name: 'favorites' })">收藏</el-button>
+          <el-button @click="$router.push({ name: 'history' })">历史</el-button>
+          <el-button @click="$router.push({ name: 'profile' })">个人资料</el-button>
+        </el-space>
+      </el-card>
+
+      <el-card shadow="never" class="status">
+        <template #header>会话状态</template>
+        <p v-if="!auth.ready">正在检测登录状态…</p>
+        <template v-else>
+          <p v-if="auth.loggedIn">
+            已登录：<strong>{{ auth.nickname || auth.userId }}</strong>
+          </p>
+          <p v-else>未登录 — 仍可使用核心功能，登录后可收藏和查看历史。</p>
+        </template>
+      </el-card>
+    </div>
   </div>
 </template>
 
@@ -71,13 +85,6 @@ function openLegacyGenerate() {
   line-height: 1.65;
   color: $text-secondary;
   font-size: 0.95rem;
-
-  code {
-    font-size: 0.85em;
-    padding: 0.1em 0.35em;
-    background: $gray-100;
-    border-radius: 4px;
-  }
 }
 
 .status {