Update sponsor section and links in docs and config

Added a new sponsors section with DigitalOcean and DartNode badges to both English and Chinese README files. Updated image tags to remove inline styles for badges. Modified the issue template config to update the public instance link and description.

.github/ISSUE_TEMPLATE/config.yml

@@ -3,9 +3,9 @@ contact_links:
   - name: 📚 存储库文档
     url: https://github.com/xixu-me/Xget/blob/main/README.md
     about: 查看完整的存储库文档和使用指南
-  - name: 🌐 公共实例
-    url: https://xget.xi-xu.me
-    about: 访问官方公共实例，开箱即用
+  - name: 🌐 URL 转换器
+    url: https://xuc.xi-xu.me
+    about: 访问官方 web 应用程序，开箱即用
   - name: 🔧 故障排除
     url: https://github.com/xixu-me/Xget/blob/main/README.md#-故障排除
     about: 查看常见问题和解决方案