The operator stamps EmptySince to time the idle auto-stop window, but the CRD's
status schema never declared it. Kubernetes pruned the field on every write
(apiserver warning: unknown field "status.emptySince"), so the timer reset to
nil on every read and idle auto-stop could never fire — a defect invisible to
the fake-client unit tests, which do not enforce the CRD schema. Found live:
the stamp was silently dropped the moment it was set.
Schema now declares emptySince (date-time) like its sibling timestamps.