Archive Project

Archive a project. From then on nothing new starts or bills inside it: requests on a credential pinned to the project, and every new piece of work attributed to it, are refused with the coded `409 project_archived`. Work already in flight is left to finish. Everything in the project stays readable and its configuration stays editable, and the project still answers by id. Idempotent: archiving an archived project is a no-op. Reverse it with the unarchive operation.