Get agent details

Retrieve detailed information for a specific agent.

Returns complete agent configuration including:
- Agent ID and name
- Agent type (inbound/outbound) and active status
- AI provider and selected voice details
- Prompt instructions and first message settings
- Language configuration (default and supported languages)
- Verified caller ID (for outbound agents)
- Created/updated timestamps

The agent must belong to your organization. Attempting to access an agent
from another organization will return 404.

Authentication:
- API key with READ or READ_WRITE permission, or
- OAuth access token granted the `agents:read` scope