Add animation keyframes for grid and shimmer effects, implement mouse position tracking for dynamic background, and create direct download API for video/audio files. Update types for download requests and responses.

lib/utils.ts

@@ -28,3 +28,8 @@ export function extractYouTubeId(url: string): string | null {
   
   return null;
 }
+
+// Validate a bare YouTube video ID (11 chars, URL-safe)
+export function isValidYouTubeId(id: string): boolean {
+  return /^[A-Za-z0-9_-]{11}$/.test(id);
+}