Deploy a Slurm cluster onto one of the team's dedicated clusters.

Team-admin gated like resize and add/remove member. The cluster must belong to team_id and have self-service enabled (checked by the service, which also pins the new cluster to this team). Node planning and claiming run before this returns, so "not enough nodes" or a port conflict is an immediate error; the Helm install continues in the background and the returned cluster starts out PENDING.