Archive Project

Archive a project. From then on nothing new starts or bills inside it: conversation and widget sessions, outbound and inbound calls, batch calls, test runs, knowledge-base imports, and synthesis or gateway requests on a credential pinned to the project are all 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.