Readiness probe on run pods for the ACP port

[ibolton336]

Run pods expose no readinessProbe, so phase=Running races ahead of :4000 actually listening; every ACP client (the shim today, the Hub next) re-solves this with dial-retry loops. Add a readinessProbe so Ready means "ACP is dialable." Small and well-scoped.

Done when:

• Ready on a run pod implies the ACP port accepts connections, letting hub/clients drop their dial-retry loops.

Depends on: none.