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.

components/dashboard/ChatDetail.tsx

@@ -130,9 +130,9 @@ export default function ChatDetail({ chatId }: { chatId: string }) {
   // Initialize audio element
   useEffect(() => {
     // Create audio element for notification sound
-    audioRef.current = new Audio('/notification.mp3');
+    audioRef.current = new Audio('/hohoho.mp3');
     
-    // Fallback if notification.mp3 doesn't exist - use browser API for a simple beep
+    // Fallback if hohoho.mp3 doesn't exist - use browser API for a simple beep
     audioRef.current.addEventListener('error', () => {
       audioRef.current = null;
     });