feat(导出文档): 支持取消导出

assets/webui/index.html

@@ -104,6 +104,7 @@
 				<div id="progressPanel" class="progress-panel" role="status" aria-live="polite" hidden>
 					<div class="progress-spinner"></div>
 					<div id="progressLabel" class="progress-label">加载中</div>
+					<button id="cancelExportButton" class="small-button" type="button" title="取消导出" aria-label="取消导出" hidden>取消</button>
 					<div class="progress-track">
 						<div id="progressBar" class="progress-bar" role="progressbar" aria-valuemin="0" aria-valuemax="100" aria-valuenow="0"></div>
 					</div>