get current app name

https://gist.github.com/Trim21/b930f98e000c7024b41de74f92d192aa#file-timeline-php-L668-L688

这里的获取用户端类型在重构版中有对应的函数吗

_Originally posted by @TWT233 in https://github.com/bangumi/server/issues/217#issuecomment-1279692516_

Compare the PHP reference in the linked gist, especially lines 668-688, with the refactored Go server and search for an existing user-agent or app-name entry point. Done means identifying the corresponding function or documenting that no equivalent exists; the issue names no repository file or test to run.

Written by the indexing model from the issue text.