添加抓取失败网址记录功能

- 新增 failed_urls 数据库表存储失败URL
- 抓取失败时自动记录URL、标题、错误信息
- 搜索页面显示失败URL列表
- 支持重试单个/全部失败URL
- 支持删除和清空失败记录
- 显示重试次数和时间

templates/search.html

@@ -82,6 +82,30 @@
             </div>
         </div>
 
+        <!-- 失败URL区域 -->
+        <div class="panel failed-urls-section">
+            <div class="panel-header">
+                <h2><i class="ri-error-warning-line"></i> 抓取失败的网址</h2>
+                <div class="panel-actions">
+                    <span id="failed-count" class="failed-count">0 条</span>
+                    <button onclick="loadFailedUrls()" class="btn btn-secondary btn-sm">
+                        <i class="ri-refresh-line"></i> 刷新
+                    </button>
+                    <button onclick="retryAllFailed()" class="btn btn-warning btn-sm">
+                        <i class="ri-restart-line"></i> 全部重试
+                    </button>
+                    <button onclick="clearFailedUrls()" class="btn btn-danger btn-sm">
+                        <i class="ri-delete-bin-line"></i> 清空
+                    </button>
+                </div>
+            </div>
+            <div class="panel-body">
+                <div id="failed-urls-list" class="failed-urls-list">
+                    <div class="empty-text">暂无失败记录</div>
+                </div>
+            </div>
+        </div>
+
         <!-- 保存进度 -->
         <div id="save-progress" class="save-progress" style="display: none;">
             <div class="progress-info">