feat: 文件下载

[architectMymine]

Description

fixes 文件下载 #41

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Before submitting the PR, please make sure you do the following

• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).

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[RainyNight9]

示例页面 card 增加左右边距，和其他页面类似，要显得美观一点

[Hongbusi]

utils/file 是文件相关的工具方法，为什么放一个 base64?
看见有一个 isIE 的判断，是兼容IE？如果是的话，可以删除这段逻辑，vue3 本身就不兼容IE。