feat: 前端UI标题栏优化与配置更新

- 更新.gitignore，添加frontend/.next/忽略
- 优化RecordModal、index、recurring、search、stats页面标题栏样式
- 新增frontend/lib/utils.js工具函数
- 更新useCategories.js钩子
- 添加代码优化计划文档

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

frontend/pages/recurring.js

@@ -7,11 +7,20 @@ import { useToast } from '../components/ToastProvider';
 import { useConfirm } from '../components/ConfirmProvider';
 import { useCategories } from '../hooks/useCategories';
 
+const DAYS = Array.from({ length: 28 }, (_, i) => i + 1);
+
 export default function Recurring() {
   const router = useRouter();
   const { showToast } = useToast();
   const { confirm } = useConfirm();
-  const { categories } = useCategories();
+  const { categories, error: categoriesError } = useCategories();
+
+  // 显示分类加载错误
+  useEffect(() => {
+    if (categoriesError) {
+      showToast('分类加载失败', { tone: 'error' });
+    }
+  }, [categoriesError]);
   const [bills, setBills] = useState([]);
   const [modalOpen, setModalOpen] = useState(false);
   const [editingBill, setEditingBill] = useState(null);
@@ -170,8 +179,6 @@ export default function Recurring() {
     }
   };
 
-  const days = Array.from({ length: 28 }, (_, index) => index + 1);
-
   const actions = (
     <button type="button" className="icon-button" aria-label="设置" onClick={() => router.push('/settings')}>
       <Icon name="settings" size={18} />
@@ -322,7 +329,7 @@ export default function Recurring() {
               <div className="form-group">
                 <label htmlFor="bill-day">日期（每月几号）</label>
                 <select id="bill-day" value={formData.day} onChange={(e) => setFormData({ ...formData, day: e.target.value })} disabled={submitting || deleting}>
-                  {days.map((day) => (
+                  {DAYS.map((day) => (
                     <option key={day} value={day}>{day} 日</option>
                   ))}
                 </select>