SMOODEV-2610: th admin org create --parent (one-shot child org)

[brentrager]

Adds --parent <ORG> to th admin org create. After creating the org, it links the new org under the parent with a manages relationship (same call as link-child) — so onboarding a child org under the master org is one command instead of create + a separate link-child.

th admin org create --name ATS --parent 8be5f5fd-...   # create + link in one shot

Context: onboarding the ATS org needed create then a manual relationship insert because there was no one-shot path. (The link-child/children commands already exist — this just saves the second step.)

Compiles clean (cargo check -p smooai-smooth-cli).

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Latest commit: fbfee61

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