fix: 解决下载文件扩展名的问题

backend/app/api/endpoints/files.py

@@ -89,10 +89,15 @@ async def download_file(
     if not os.path.exists(file.processed_path):
         raise HTTPException(status_code=404, detail="Processed file not found")
     
+    # Get the original filename without extension and add .md extension
+    original_filename = file.filename
+    filename_without_ext = os.path.splitext(original_filename)[0]
+    download_filename = f"{filename_without_ext}.md"
+    
     return FileResponse(
         path=file.processed_path,
-        filename=file.filename,
-        media_type="application/octet-stream"
+        filename=download_filename,
+        media_type="text/markdown"
     )
 
 @router.websocket("/ws/status/{file_id}")