feat: PDF对比用iframe显示原PDF文件（支持扫描版PDF）

templates/translation.html

@@ -84,11 +84,21 @@
                     const response = await fetch(`/api/compare/${translationId}`);
                     const result = await response.json();
                     
+                    // 原文面板：如果有PDF URL用iframe显示，否则显示提取的文本
+                    let originalHtml = '';
+                    if (result.original_pdf_url) {
+                        originalHtml = `<iframe src="${result.original_pdf_url}" style="width:100%;height:500px;border:none;"></iframe>`;
+                    } else if (result.original && result.original.length > 0) {
+                        originalHtml = `<div style="white-space:pre-wrap;font-family:monospace;">${escapeHtml(result.original)}</div>`;
+                    } else {
+                        originalHtml = '<div class="text-muted">原文内容未找到（可能PDF已被删除）</div>';
+                    }
+                    
                     document.getElementById('resultContent').innerHTML = `
                         <div class="compare-container">
                             <div class="compare-panel original">
-                                <h5>原文</h5>
-                                <div>${escapeHtml(result.original)}</div>
+                                <h5>原文 PDF</h5>
+                                ${originalHtml}
                             </div>
                             <div class="compare-panel translated">
                                 <h5>译文</h5>
@@ -98,7 +108,7 @@
                     `;
                     
                 } catch (error) {
-                    alert('加载对比失败');
+                    alert('加载对比失败: ' + error.message);
                 }
             } else {
                 loadResult();