fix: SFTP下载使用新窗口打开直链

- app.js downloadFile: SFTP有直链时用window.open新窗口打开
- share.html downloadFile: 分享页面同样处理
- 本地存储下载保持原有方式不变
- 解决HTTPS页面下载HTTP直链的Mixed Content问题

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

frontend/app.html

@@ -2541,6 +2541,6 @@
     }
   </style>
 
-  <script src="app.js?v=20251127001"></script>
+  <script src="app.js?v=20251127003"></script>
 </body>
 </html>