List agents

{
    "agents": [
        {
            "id": "a1b2c3d4-0000-0000-0000-000000000001",
            "tenant_id": "11111111-1111-1111-1111-111111111111",
            "name": "Support Agent",
            "description": "Handles inbound customer support",
            "voice": "marin",
            "temperature": 0.8,
            "is_active": true,
            "created_at": "2026-06-01T10:00:00.000Z",
            "tools": []
        }
    ]
}