fix: Mp4Muxer name collision (self-shadowing destructure)

index.html

@@ -439,7 +439,7 @@
     let currentSong = null;
 
     // ── Fast video generation (WebCodecs + MP4 muxer) ─────────────────────
-    const { Muxer: Mp4Muxer, ArrayBufferTarget } = Mp4Muxer;
+    const { Muxer: Mp4MuxerClass, ArrayBufferTarget } = Mp4Muxer;
 
     async function generateShareVideo(song, btn) {
       const origHTML = btn.innerHTML;
@@ -555,7 +555,7 @@
 
         // ── Encode with WebCodecs + MP4 muxer ──
         const target = new ArrayBufferTarget();
-        const muxer = new Mp4Muxer({
+        const muxer = new Mp4MuxerClass({
           target,
           video: { codec: "avc", width: W, height: H },
           audio: { codec: "aac", sampleRate, numberOfChannels: numChannels },