Consider renaming @server and @client for windows compatability

[ealmloff]

Issue

The CLI currently accepts @ arguments to pass different args to different builds. Unfortunately, @ has a special meaning in powershell on windows which can result in some confusing errors. On windows, it can also mean splatting

We could use another symbol like ?.

Workarounds

If you find this issue after running into the above error, surrounding @server or @client in quotes fixes the issue:

dx serve "@server" --server

[jarjk]

doesn't ? correspond to single-char glob in posix shells? wouldn't that ruin it then?