fix: install lamejs from GitHub repo for proper browser support

Switched from npm package to GitHub repo (github:zhuker/lamejs) which
includes the proper browser build. Reverted to simple dynamic import.

Fixes MP3 export MPEGMode reference error.

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

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

lib/audio/export.ts

@@ -129,31 +129,6 @@ 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
  */
@@ -161,8 +136,8 @@ export async function audioBufferToMp3(
   audioBuffer: AudioBuffer,
   options: ExportOptions = { format: 'mp3', bitrate: 192 }
 ): Promise<ArrayBuffer> {
-  // Load lamejs library
-  const lamejs = await loadLamejs();
+  // Dynamically import lamejs from GitHub repo (has proper browser build)
+  const lamejs = await import('lamejs');
 
   const { bitrate = 192, normalize } = options;
   const numberOfChannels = Math.min(audioBuffer.numberOfChannels, 2); // MP3 supports max 2 channels