Implement testing framework with Vitest, add unit tests for API routes and utility functions, and configure CI workflow for automated testing. Update package dependencies for testing libraries and add test scripts to package.json.

lib/youtube.ts

@@ -1,6 +1,6 @@
 import { exec } from 'child_process';
 import { promisify } from 'util';
-import { readFile, unlink, mkdir, copyFile } from 'fs/promises';
+import { unlink, mkdir, copyFile } from 'fs/promises';
 import { existsSync } from 'fs';
 import path from 'path';
 import type { VideoInfo, FormatOption, DownloadRequest, DownloadResponse } from './types';
@@ -22,8 +22,7 @@ function getFfmpegLocationFlag(): string {
 const DOWNLOADS_DIR = path.join(process.cwd(), 'downloads');
 const PUBLIC_DOWNLOADS_DIR = path.join(process.cwd(), 'public', 'downloads');
 
-// Sanitize filename for safe storage
-function sanitizeFilename(filename: string): string {
+export function sanitizeFilename(filename: string): string {
   return filename
     .replace(/[^a-z0-9]/gi, '_')
     .replace(/_+/g, '_')