feature: allow dashes in new folder names

[ericbstie]

In the UI it's not possible to create a folder with dashes (-) in the name directly:

It is however possible to create folders with dashes in them locally, or by typing slashes in the file name:

It's nice to have dashes in folder names because that's the naming convention for npm packages:

import { sharedLogicFunction } from "../folder-name/logic.ts";