Not sure about the kata editor, but you can create your own kata once you get at least 25 honor (which you have); just hover over your score in the top right corner and you should also get a "New Kata" item.

If not, report it here.

To fork, usually you get to do that once you solved it, then you can fork a solution (including the one of the author), like here; otherwise, just add "/forks" to the basic kata url.

Hope this helps :)

How can I fork a Kata?

Why can't I see the Kata editor in the profile menu?

It would be nice if you could allow loading NuGet packages (as on the .NET Fiddle site) or at least provide both NUnit and xUnit.net