fix: 个人库存页未登录时显示登录引导

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/views/Inventory.vue

@@ -1,5 +1,11 @@
 <template>
   <div class="inventory-page">
+    <!-- Login prompt -->
+    <div v-if="!auth.isLoggedIn" class="login-prompt">
+      <p>登录后可管理个人库存、获取购油方案</p>
+      <button class="btn-primary" @click="ui.openLogin()">登录 / 注册</button>
+    </div>
+    <template v-else>
     <!-- My Oil Plan -->
     <template v-if="auth.isLoggedIn">
       <!-- Active plan: show shopping list -->
@@ -160,6 +166,7 @@
     <div v-else class="empty-hint">
       {{ ownedOils.length ? '暂无完全匹配的配方' : '添加精油后自动推荐配方' }}
     </div>
+    </template>
   </div>
 </template>
 
@@ -664,6 +671,8 @@ onMounted(async () => {
 .overlay-header h3 { margin: 0; font-size: 16px; }
 .form-label { display: block; font-size: 13px; color: #6b6375; margin-bottom: 4px; font-weight: 500; }
 .form-textarea { width: 100%; border: 1.5px solid #e5e4e7; border-radius: 8px; padding: 8px; font-size: 13px; font-family: inherit; resize: vertical; box-sizing: border-box; }
+.login-prompt { text-align: center; padding: 60px 20px; color: #6b6375; }
+.login-prompt p { margin-bottom: 16px; font-size: 15px; }
 .plan-pending-hint { font-size: 11px; color: #b0aab5; margin-top: 4px; }
 .teacher-matched { color: #2e7d5a; font-size: 13px; margin-top: 4px; font-weight: 500; }
 .teacher-no-match { color: #c62828; font-size: 12px; margin-top: 4px; }