Per review: RESTARTABLE_INFRA_CONTAINERS and the new CONTROLLABLE_INFRA_CONTAINERS
were near-identical subsets of SIBLING_CONTAINERS. Drop both and validate infra
lifecycle ops against SIBLING_CONTAINERS directly (all four infra containers;
hive-c0re is never in it, so it can't stop itself). This also makes hive-matrix
restartable, including via an infra_admin agent's restart tool.
Collapse the two priv ops too: RestartInfraContainer is gone; ControlInfraContainer
{ action } is the single op (restart = action: Restart). priv_client's
restart_infra_container is now a thin wrapper over control_infra_container.
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