feat: use png favicon as fallback

index.html

@@ -3,6 +3,7 @@
   <head>
     <meta charset="UTF-8" />
     <link rel="icon" type="image/svg+xml" href="/favicon.svg" />
+    <link rel="icon" type="image/png" href="/favicon.png" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
     <title>MelodyMuse – Suno Song Asset Generator</title>
   </head>