feat: add MP3 and FLAC export formats

Implemented Phase 11.1 export format support:
- Added MP3 export using lamejs library
- Added FLAC export using fflate DEFLATE compression
- Updated ExportDialog with format selector and format-specific options
  - MP3: bitrate selector (128/192/256/320 kbps)
  - FLAC: compression quality slider (0-9)
  - WAV: bit depth selector (16/24/32-bit)
- Updated AudioEditor to route export based on selected format
- Created TypeScript declarations for lamejs
- Fixed AudioStatistics to use audioBuffer instead of buffer property

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

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

components/analysis/AudioStatistics.tsx

@@ -33,20 +33,20 @@ export function AudioStatistics({ tracks, className }: AudioStatisticsProps) {
     let channels = 0;
 
     tracks.forEach(track => {
-      if (!track.buffer) return;
+      if (!track.audioBuffer) return;
 
-      const duration = track.buffer.duration;
+      const duration = track.audioBuffer.duration;
       maxDuration = Math.max(maxDuration, duration);
 
       // Get sample rate and channels from first track
       if (sampleRate === 0) {
-        sampleRate = track.buffer.sampleRate;
-        channels = track.buffer.numberOfChannels;
+        sampleRate = track.audioBuffer.sampleRate;
+        channels = track.audioBuffer.numberOfChannels;
       }
 
       // Calculate peak and RMS from buffer
-      for (let ch = 0; ch < track.buffer.numberOfChannels; ch++) {
-        const channelData = track.buffer.getChannelData(ch);
+      for (let ch = 0; ch < track.audioBuffer.numberOfChannels; ch++) {
+        const channelData = track.audioBuffer.getChannelData(ch);
         let chPeak = 0;
         let chRmsSum = 0;