style: 將詞卡數目統計顯示調整為右對齊

- 修改詞卡數量統計的對齊方式從左對齊改為右對齊
- 提升頁面佈局的視覺平衡

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

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

frontend/app/flashcards/page.tsx

@@ -237,7 +237,7 @@ function FlashcardsContent() {
         />
 
         {/* 詞卡數目統計 */}
-        <div className="flex justify-between items-center mb-4">
+        <div className="flex justify-end items-center mb-4">
           <h3 className="text-lg font-semibold">
             共 {searchState.pagination.totalCount} 個詞卡
             {searchState.pagination.totalPages > 1 && (