feat(前端界面): 提示信息添加PDF

assets/webui/index.html

@@ -611,7 +611,7 @@
 			</aside>
 
 			<section class="viewer-panel" tabindex="0" aria-label="阅读区">
-				<div id="emptyState" class="empty-state">选择 OFD 文件</div>
+				<div id="emptyState" class="empty-state">选择 OFD、PDF 文件</div>
 				<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>