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>

backend/app/routers/translate.py

@@ -507,16 +507,18 @@ async def delete_translation(
 async def download_translated_pdf(
     task_id: str,
     lang: str = Query(..., description="Target language code"),
+    format: str = Query("reflow", description="PDF format: 'layout' or 'reflow'"),
     db: Session = Depends(get_db),
     current_user: User = Depends(get_current_user)
 ):
     """
-    Download a translated PDF with layout preservation.
+    Download a translated PDF.
 
     - **task_id**: Task UUID
     - **lang**: Target language code (e.g., 'en', 'ja')
+    - **format**: PDF format - 'layout' (preserves positions with text wrapping) or 'reflow' (flowing layout)
 
-    Returns PDF file with translated content preserving original layout.
+    Returns PDF file with translated content.
     """
     from app.services.pdf_generator_service import pdf_generator_service
     from app.services.translation_service import list_available_translations
@@ -587,26 +589,37 @@ async def download_translated_pdf(
             detail="Invalid translation file format"
         )
 
+    # Validate format parameter
+    use_layout = format.lower() == 'layout'
+
     # Generate translated PDF to temp file
-    output_filename = f"{task_id}_translated_{lang}.pdf"
+    format_suffix = '_layout' if use_layout else '_reflow'
+    output_filename = f"{task_id}_translated_{lang}{format_suffix}.pdf"
 
     with tempfile.NamedTemporaryFile(suffix='.pdf', delete=False) as tmp_file:
         output_path = Path(tmp_file.name)
 
     try:
-        # Get source file path for images if available
-        source_file_path = None
-        if task.files and len(task.files) > 0:
-            stored_path = task.files[0].stored_path
-            if stored_path and Path(stored_path).exists():
-                source_file_path = Path(stored_path)
+        # Use result_dir as image source (contains extracted images)
+        image_dir = result_json_path.parent
 
-        success = pdf_generator_service.generate_translated_pdf(
-            result_json_path=result_json_path,
-            translation_json_path=translation_file,
-            output_path=output_path,
-            source_file_path=source_file_path
-        )
+        # Choose PDF generation method based on format
+        if use_layout:
+            # Layout mode: preserve original positions with text wrapping
+            success = pdf_generator_service.generate_translated_layout_pdf(
+                result_json_path=result_json_path,
+                translation_json_path=translation_file,
+                output_path=output_path,
+                source_file_path=image_dir
+            )
+        else:
+            # Reflow mode: flowing layout
+            success = pdf_generator_service.generate_translated_pdf(
+                result_json_path=result_json_path,
+                translation_json_path=translation_file,
+                output_path=output_path,
+                source_file_path=image_dir
+            )
 
         if not success:
             raise HTTPException(