Switch notification sound to hohoho.mp3 and add download script

Replaced all references to notification.mp3 with hohoho.mp3 in notification-related components and context. Added hohoho.mp3 to the public directory. Introduced a script (download-notification-sound.js) for downloading notification sounds from YouTube using @distube/ytdl-core, which was added as a devDependency. Also added yt-dlp.exe for alternative audio downloading.

lib/notification-context.tsx

@@ -92,7 +92,7 @@ export function NotificationProvider({ children }: NotificationProviderProps) {
     }
 
     // Initialize audio
-    audioRef.current = new Audio('/notification.mp3');
+    audioRef.current = new Audio('/hohoho.mp3');
     audioRef.current.addEventListener('error', () => {
       audioRef.current = null;
     });