/**
 * Format a byte count into a human-readable file size string.
 * Uses binary units (1 KB = 1024 bytes).
 */
export declare const formatFileSize: (bytes: number) => string;
/**
 * Extract the file extension from a filename, lowercase.
 * Returns null if no extension is present.
 */
export declare const getFileExtension: (filename: string) => string | null;
