feat: 在搜尋控制與詞卡清單間添加詞卡數目統計顯示

- 添加詞卡總數和當前頁面詞卡數量顯示
- 支援分頁時顯示頁面信息
- 添加快取狀態指示器
- 提升用戶對搜尋結果的認知

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

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

frontend/app/flashcards/page.tsx

@@ -236,6 +236,23 @@ function FlashcardsContent() {
           setShowAdvancedSearch={setShowAdvancedSearch}
         />
 
+        {/* 詞卡數目統計 */}
+        <div className="flex justify-between items-center mb-4">
+          <h3 className="text-lg font-semibold">
+            共 {searchState.pagination.totalCount} 個詞卡
+            {searchState.pagination.totalPages > 1 && (
+              <span className="text-sm font-normal text-gray-600 ml-2">
+                (第 {searchState.pagination.currentPage} 頁，顯示 {searchState.flashcards.length} 個)
+              </span>
+            )}
+          </h3>
+          {searchState.cacheHit && (
+            <span className="text-xs text-green-600 bg-green-50 px-2 py-1 rounded-full">
+              快取
+            </span>
+          )}
+        </div>
+
         {/* Search Results */}
         <SearchResults
           searchState={searchState}