Get Health Summary

{
    "system": {
        "overall_status": "healthy",
        "total_providers": 0,
        "healthy_providers": 0,
        "degraded_providers": 0,
        "unhealthy_providers": 0,
        "total_models": 0,
        "healthy_models": 0,
        "degraded_models": 0,
        "unhealthy_models": 0,
        "system_uptime": 0,
        "last_updated": "2019-08-24T14:15:22Z"
    },
    "providers": [
        {
            "provider": "string",
            "gateway": "string",
            "status": "online",
            "total_models": 0,
            "healthy_models": 0,
            "degraded_models": 0,
            "unhealthy_models": 0,
            "avg_response_time_ms": 0,
            "overall_uptime": 0,
            "last_checked": "2019-08-24T14:15:22Z",
            "error_message": "string"
        }
    ],
    "models": [
        {
            "model_id": "string",
            "provider": "string",
            "gateway": "string",
            "status": "healthy",
            "response_time_ms": 0,
            "success_rate": 0,
            "last_checked": "2019-08-24T14:15:22Z",
            "last_success": "2019-08-24T14:15:22Z",
            "last_failure": "2019-08-24T14:15:22Z",
            "error_count": 0,
            "total_requests": 0,
            "avg_response_time_ms": 0,
            "uptime_percentage": 0,
            "error_message": "string"
        }
    ],
    "monitoring_active": false,
    "last_check": "2019-08-24T14:15:22Z"
}