fix: use direct ES module imports from lamejs source files

Fixed MP3 export by importing lamejs modules directly from source:
- Import MPEGMode, Lame, and BitStream from individual source files
- Use Lame API directly instead of Mp3Encoder wrapper
- Updated TypeScript declarations for each module
- Resolves "MPEGMode is not defined" error

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

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

lib/audio/export.ts

@@ -136,8 +136,12 @@ export async function audioBufferToMp3(
   audioBuffer: AudioBuffer,
   options: ExportOptions = { format: 'mp3', bitrate: 192 }
 ): Promise<ArrayBuffer> {
-  // Dynamically import lamejs from GitHub repo (has proper browser build)
-  const lamejs = await import('lamejs');
+  // Import lamejs modules directly
+  const [{ default: MPEGMode }, { default: Lame }, { default: BitStream }] = await Promise.all([
+    import('lamejs/src/js/MPEGMode'),
+    import('lamejs/src/js/Lame'),
+    import('lamejs/src/js/BitStream'),
+  ]);
 
   const { bitrate = 192, normalize } = options;
   const numberOfChannels = Math.min(audioBuffer.numberOfChannels, 2); // MP3 supports max 2 channels
@@ -167,26 +171,51 @@ export async function audioBufferToMp3(
     rightPcm[i] = Math.max(-32768, Math.min(32767, (right[i] / peak) * 32767));
   }
 
-  // Encode
-  const mp3encoder = new lamejs.Mp3Encoder(numberOfChannels, sampleRate, bitrate);
+  // Create encoder using lamejs modules
+  const lame = new Lame();
+  const gfp = lame.lame_init();
+
+  gfp.num_channels = numberOfChannels;
+  gfp.in_samplerate = sampleRate;
+  gfp.brate = bitrate;
+  gfp.mode = numberOfChannels === 1 ? MPEGMode.MONO : MPEGMode.STEREO;
+  gfp.quality = 3; // 0=best (very slow), 9=worst (fast)
+  gfp.write_id3tag_automatic = 0;
+
+  lame.lame_init_params(gfp);
+
   const mp3Data: Int8Array[] = [];
+  const mp3buf = new Int8Array(samples * 1.25 + 7200); // Estimate output size
   const sampleBlockSize = 1152; // Standard MP3 frame size
 
   for (let i = 0; i < samples; i += sampleBlockSize) {
-    const leftChunk = leftPcm.subarray(i, i + sampleBlockSize);
-    const rightChunk = numberOfChannels > 1 ? rightPcm.subarray(i, i + sampleBlockSize) : leftChunk;
-    const mp3buf = mp3encoder.encodeBuffer(leftChunk, rightChunk);
-    if (mp3buf.length > 0) {
-      mp3Data.push(mp3buf);
+    const leftChunk = leftPcm.subarray(i, Math.min(i + sampleBlockSize, samples));
+    const rightChunk = numberOfChannels > 1
+      ? rightPcm.subarray(i, Math.min(i + sampleBlockSize, samples))
+      : leftChunk;
+
+    const bytesEncoded = lame.lame_encode_buffer(
+      gfp,
+      leftChunk,
+      rightChunk,
+      leftChunk.length,
+      mp3buf,
+      0
+    );
+
+    if (bytesEncoded > 0) {
+      mp3Data.push(new Int8Array(mp3buf.subarray(0, bytesEncoded)));
     }
   }
 
   // Flush remaining data
-  const mp3buf = mp3encoder.flush();
-  if (mp3buf.length > 0) {
-    mp3Data.push(mp3buf);
+  const flushBytes = lame.lame_encode_flush(gfp, mp3buf, 0);
+  if (flushBytes > 0) {
+    mp3Data.push(new Int8Array(mp3buf.subarray(0, flushBytes)));
   }
 
+  lame.lame_close(gfp);
+
   // Combine all chunks
   const totalLength = mp3Data.reduce((acc, arr) => acc + arr.length, 0);
   const result = new Uint8Array(totalLength);