Creating a content app by the tutorial and analyzing the configuration of the actions i saw these to action classes:
[1] info.magnolia.ui.contentapp.detail.action.CreateItemActionDefinition
[2] info.magnolia.ui.app.contacts.action.AddFolderActionDefinition

Naming inconsistency:
Either create or add for both classes, preferably create.

Location:
Creating a folder should be prided by the contentapp module and not by the contacts module.