Schedule an outbound call to a contact

Queues an outbound call targeted at this contact. Wraps POST /calls/schedule and auto-fills phoneNumber from the contact record, plus injects contact context (name, tags, last interaction) so the agent knows who it's calling. The resulting Call is linked to the contact — shows up in their timeline, counts toward lifecycle stats. Agent must be isActive and owned by the caller; contact must have a valid E.164 phone.