Function validate_group_deletion 

pub async fn validate_group_deletion(
    infra: &InfraContext<'_>,
    token: &str,
    label: &str,
) -> Result<(), Error>

Check that deleting label would not leave any node without a group.

An xname is “orphaned” if label is its only HSM group. When at least one such node exists, returns Error::Conflict listing the orphans so the operator can decide whether to move them first or pass force to delete_group.