Sandbox only: open or move a dispute on a paid payment

The first call opens one synthetic chargeback (dispute.created); later calls move it (dispute.updated, or dispute.closed for won and lost). Responding to it with evidence is not simulated. The provider never sees this outcome; the real handlers apply it, so the real events follow. 404 resource_not_available outside the sandbox; 409 state_conflict when the object is past this step.