create_agent_identity
Create a new agent machine identity and return its API key.
The raw key is returned ONCE in this response and never again — store it securely immediately. The key is prefixed with "vib_" and stored as a SHA-256 hash in VibOps. If the key is lost, rotate the identity instead of recreating it.
Write operation — recorded in the audit log.
Args: name: Human-readable label for this identity (e.g. "pricing-agent-prod"). expires_at: Optional expiry date in ISO 8601 format (e.g. "2027-01-01T00:00:00Z"). If omitted, the identity does not expire.