ProcessResultDto

{
    "s3_key": "exports/abc12345/csv_export.csv",
    "s3_url": "https://...",
    "file_size": 2048576,
    "format": "csv",
    "encoding": "utf8",
    "imported": 100,
    "updated": 50,
    "failed": 5,
    "errors": [
        {
            "external_user_id": "12345",
            "error": "User not found"
        }
    ],
    "duration_ms": 15420
}