fix: update system update icon and speed limit input

[xionglinlin]

1. Replaced system update icon with a new design using blue gradient and simplified shape
2. Added input validation for download speed limit setting
3. Implemented real-time model update for speed limit configuration
4. Added key handling for Enter key in speed limit input field
5. Improved user feedback with alert messages for invalid inputs

fix: 更新系统更新图标和速度限制输入

1. 使用蓝色渐变和简化形状重新设计了系统更新图标
2. 为下载速度限制设置添加了输入验证
3. 实现了速度限制配置的实时模型更新
4. 为速度限制输入字段添加了回车键处理
5. 通过无效输入的警报消息改进了用户反馈

pms: Bug-313015
pms: Bug-313021
pms: Bug-313027
pms: Bug-313043
pms: Bug-314877

[deepin-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: robertkill, xionglinlin

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