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>

package.json

@@ -10,6 +10,7 @@
   },
   "dependencies": {
     "clsx": "^2.1.1",
+    "fflate": "^0.8.2",
     "lamejs": "^1.2.1",
     "lucide-react": "^0.553.0",
     "next": "^16.0.0",