refactor: 更新導航標籤為設計頁面

- 將🧪測試改為🎨設計
- 路由從/review-tests改為/review-design

🤖 Generated with [Claude Code](https://claude.ai/code)

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

frontend/components/Navigation.tsx

@@ -19,7 +19,7 @@ export function Navigation({ showExitLearning = false, onExitLearning }: Navigat
     { href: '/dashboard', label: '儀表板' },
     { href: '/flashcards', label: '詞卡' },
     { href: '/review', label: '複習' },
-    { href: '/review-tests', label: '🧪 測試' },
+    { href: '/review-design', label: '🎨 設計' },
     { href: '/generate', label: 'AI 生成' },
     { href: '/settings', label: '⚙️ 設定' }
   ]