Agent Automation Activity Catalogue

Every activity kind that can go in an automation, with the JSON-Schema of its config. Read this before building one: the schema is what tells you which fields a step needs, and it is generated from the same registry the executor dispatches on, so it cannot drift from what will actually run.

Also flags which kinds send mail and which write or destroy data, because the catalogue is the only place an agent can learn that before it commits a step to an automation somebody then has to approve running.