feat: add translated PDF format selection (layout/reflow)

- Add generate_translated_layout_pdf() method for layout-preserving translated PDFs
- Add generate_translated_pdf() method for reflow translated PDFs
- Update translate router to accept format parameter (layout/reflow)
- Update frontend with dropdown to select translated PDF format
- Fix reflow PDF table cell extraction from content dict
- Add embedded images handling in reflow PDF tables
- Archive improve-translated-text-fitting openspec proposal

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

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

frontend/src/pages/TaskDetailPage.tsx

@@ -178,13 +178,31 @@ export default function TaskDetailPage() {
     }
   }
 
-  const handleDownloadPDF = async () => {
+  const handleDownloadLayoutPDF = async () => {
     if (!taskId) return
     try {
-      await apiClientV2.downloadPDF(taskId)
+      await apiClientV2.downloadPDF(taskId, 'layout')
       toast({
         title: t('export.exportSuccess'),
-        description: 'PDF 已下載',
+        description: '版面 PDF 已下載',
+        variant: 'success',
+      })
+    } catch (error: any) {
+      toast({
+        title: t('export.exportError'),
+        description: error.response?.data?.detail || t('errors.networkError'),
+        variant: 'destructive',
+      })
+    }
+  }
+
+  const handleDownloadReflowPDF = async () => {
+    if (!taskId) return
+    try {
+      await apiClientV2.downloadPDF(taskId, 'reflow')
+      toast({
+        title: t('export.exportSuccess'),
+        description: '流式 PDF 已下載',
         variant: 'success',
       })
     } catch (error: any) {
@@ -328,13 +346,14 @@ export default function TaskDetailPage() {
     }
   }
 
-  const handleDownloadTranslatedPdf = async (lang: string) => {
+  const handleDownloadTranslatedPdf = async (lang: string, format: 'layout' | 'reflow' = 'reflow') => {
     if (!taskId) return
     try {
-      await apiClientV2.downloadTranslatedPdf(taskId, lang)
+      await apiClientV2.downloadTranslatedPdf(taskId, lang, format)
+      const formatLabel = format === 'layout' ? '版面' : '流式'
       toast({
         title: '下載成功',
-        description: `翻譯 PDF (${lang}) 已下載`,
+        description: `翻譯 ${formatLabel} PDF (${lang}) 已下載`,
         variant: 'success',
       })
     } catch (error: any) {
@@ -513,7 +532,7 @@ export default function TaskDetailPage() {
             </CardTitle>
           </CardHeader>
           <CardContent>
-            <div className="grid grid-cols-2 md:grid-cols-4 gap-3">
+            <div className="grid grid-cols-2 md:grid-cols-5 gap-3">
               <Button onClick={handleDownloadJSON} variant="outline" className="gap-2 h-20 flex-col">
                 <FileJson className="w-8 h-8" />
                 <span>JSON</span>
@@ -526,9 +545,13 @@ export default function TaskDetailPage() {
                 <FileText className="w-8 h-8" />
                 <span>Markdown</span>
               </Button>
-              <Button onClick={handleDownloadPDF} className="gap-2 h-20 flex-col">
+              <Button onClick={handleDownloadLayoutPDF} className="gap-2 h-20 flex-col">
                 <Download className="w-8 h-8" />
-                <span>PDF</span>
+                <span>版面 PDF</span>
+              </Button>
+              <Button onClick={handleDownloadReflowPDF} variant="outline" className="gap-2 h-20 flex-col">
+                <Download className="w-8 h-8" />
+                <span>流式 PDF</span>
               </Button>
             </div>
           </CardContent>
@@ -542,7 +565,6 @@ export default function TaskDetailPage() {
             <CardTitle className="flex items-center gap-2">
               <Languages className="w-5 h-5" />
               文件翻譯
-              <Badge variant="secondary" className="ml-2">MADLAD-400</Badge>
             </CardTitle>
           </CardHeader>
           <CardContent className="space-y-4">
@@ -624,15 +646,22 @@ export default function TaskDetailPage() {
                           <Download className="w-3 h-3" />
                           JSON
                         </Button>
-                        <Button
-                          variant="default"
-                          size="sm"
-                          onClick={() => handleDownloadTranslatedPdf(item.target_lang)}
-                          className="gap-1"
+                        <Select
+                          onValueChange={(format: 'layout' | 'reflow') =>
+                            handleDownloadTranslatedPdf(item.target_lang, format)
+                          }
                         >
-                          <FileOutput className="w-3 h-3" />
-                          PDF
-                        </Button>
+                          <SelectTrigger className="w-[100px] h-8">
+                            <div className="flex items-center gap-1">
+                              <FileOutput className="w-3 h-3" />
+                              <span className="text-xs">PDF</span>
+                            </div>
+                          </SelectTrigger>
+                          <SelectContent>
+                            <SelectItem value="layout">版面 PDF</SelectItem>
+                            <SelectItem value="reflow">流式 PDF</SelectItem>
+                          </SelectContent>
+                        </Select>
                         <Button
                           variant="ghost"
                           size="sm"
@@ -649,7 +678,7 @@ export default function TaskDetailPage() {
             )}
 
             <p className="text-xs text-muted-foreground">
-              使用 MADLAD-400-3B 模型進行翻譯，支援 450+ 種語言。首次翻譯需要載入模型（約 10-30 秒）。
+              使用雲端翻譯服務進行多語言翻譯，支援多種目標語言。
             </p>
           </CardContent>
         </Card>