Archive a project

The project Owner or Manager, or org.compliance.manage (403 otherwise). Only a COMPLETED or CANCELLED project (409 PROJECT_NOT_CLOSED); 409 ALREADY_ARCHIVED when it already is. Archive is a flag, not a status: the project keeps its status, is hidden from project lists by default, and refuses any status change (409 PROJECT_ARCHIVED) until unarchived. Runs the readiness gate with transition ARCHIVE under the organization's enforcement mode: in BLOCK a required gap answers 409 READINESS_GAPS { error, code, requiredGaps, checkId, transition }; in WARN the archive goes through and readiness carries the verdict. Audited as PROJECT_ARCHIVED. Returns { projectId, status, archivedAt, archivedBy { id, name } | null, readiness { mode, passed, requiredGaps, checkId, transition } | null }.