List files for a book

{
    "files": [
        {
            "id": "f1a2b3c4-d5e6-7890-abcd-ef1234567890",
            "bookId": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
            "languageId": 1,
            "fileType": "pdf",
            "sourceType": "local",
            "filePath": "storage/books/files/the-great-controversy/en/gc-en.pdf",
            "cloudUrl": null,
            "cloudDirectUrl": null,
            "fileName": "gc-en.pdf",
            "fileSizeBytes": 5242880,
            "mimeType": "application/pdf",
            "downloadCount": 320,
            "isActive": 1,
            "uploadedAt": "2026-02-01T10:00:00.000Z",
            "languageCode": "en",
            "languageName": "English"
        }
    ]
}