fix: load lamejs from pre-built browser bundle

Changed MP3 export to dynamically load the pre-built lame.min.js
bundle from node_modules instead of trying to import the CommonJS
module. The browser bundle properly bundles all dependencies including
MPEGMode and exposes a global lamejs object.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

lib/audio/export.ts

@@ -129,6 +129,31 @@ export function downloadArrayBuffer(
   URL.revokeObjectURL(url);
 }
 
+/**
+ * Load lamejs library dynamically
+ */
+async function loadLamejs(): Promise<any> {
+  // Check if already loaded
+  if (typeof window !== 'undefined' && (window as any).lamejs) {
+    return (window as any).lamejs;
+  }
+
+  // Load the script from node_modules
+  return new Promise((resolve, reject) => {
+    const script = document.createElement('script');
+    script.src = '/node_modules/.pnpm/lamejs@1.2.1/node_modules/lamejs/lame.min.js';
+    script.onload = () => {
+      if ((window as any).lamejs) {
+        resolve((window as any).lamejs);
+      } else {
+        reject(new Error('lamejs failed to load'));
+      }
+    };
+    script.onerror = () => reject(new Error('Failed to load lamejs script'));
+    document.head.appendChild(script);
+  });
+}
+
 /**
  * Convert an AudioBuffer to MP3
  */
@@ -136,9 +161,8 @@ export async function audioBufferToMp3(
   audioBuffer: AudioBuffer,
   options: ExportOptions = { format: 'mp3', bitrate: 192 }
 ): Promise<ArrayBuffer> {
-  // Dynamically import lamejs - use default export for CommonJS compatibility
-  const lameModule = await import('lamejs');
-  const lamejs = lameModule.default || lameModule;
+  // Load lamejs library
+  const lamejs = await loadLamejs();
 
   const { bitrate = 192, normalize } = options;
   const numberOfChannels = Math.min(audioBuffer.numberOfChannels, 2); // MP3 supports max 2 channels