improve(git-changelog): support mapAuthors for authors in front matter during dev

[northword]

In build mode, the authors returned by useChangelog() is a complete list of authors, so authors in the front matter can be retrieved with their details (avatars, links, etc.), since the complete Git record is retrieved.

However, under dev, since the VirtualModule only contains data for the current page, the authors in the front matter may not be included in changelog.authors, so their details are not available.

We may need to change the logic to get the front matter of the md file on the vite side instead of the client side.