feat: add export scope options (project/selection/tracks)

Implemented Phase 11.3 - Export Regions:
- Added export scope selector in ExportDialog
  - Entire Project: Mix all tracks into single file
  - Selected Region: Export only the selected region (disabled if no selection)
  - Individual Tracks: Export each track as separate file
- Updated ExportSettings interface with scope property
- Refactored handleExport to support all three export modes:
  - Project mode: Mix all tracks (existing behavior)
  - Selection mode: Extract selection from all tracks and mix
  - Tracks mode: Loop through tracks and export separately with sanitized filenames
- Added hasSelection prop to ExportDialog to enable/disable selection option
- Created helper function convertAndDownload to reduce code duplication
- Selection mode uses extractBufferSegment for precise region extraction
- Track names are sanitized for filenames (remove special characters)

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

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

components/editor/AudioEditor.tsx

@@ -730,57 +730,113 @@ export function AudioEditor() {
     setIsExporting(true);
 
     try {
-      // Get max duration and sample rate
-      const maxDuration = getMaxTrackDuration(tracks);
       const sampleRate = tracks[0]?.audioBuffer?.sampleRate || 44100;
 
-      // Mix all tracks into a single buffer
-      const mixedBuffer = mixTracks(tracks, sampleRate, maxDuration);
+      // Helper function to convert and download a buffer
+      const convertAndDownload = async (buffer: AudioBuffer, filename: string) => {
+        let exportedBuffer: ArrayBuffer;
+        let mimeType: string;
+        let fileExtension: string;
 
-      // Convert based on format
-      let exportedBuffer: ArrayBuffer;
-      let mimeType: string;
-      let fileExtension: string;
+        if (settings.format === 'mp3') {
+          exportedBuffer = await audioBufferToMp3(buffer, {
+            format: 'mp3',
+            bitrate: settings.bitrate,
+            normalize: settings.normalize,
+          });
+          mimeType = 'audio/mpeg';
+          fileExtension = 'mp3';
+        } else if (settings.format === 'flac') {
+          exportedBuffer = await audioBufferToFlac(buffer, {
+            format: 'flac',
+            bitDepth: settings.bitDepth,
+            quality: settings.quality,
+            normalize: settings.normalize,
+          });
+          mimeType = 'application/octet-stream';
+          fileExtension = 'flac';
+        } else {
+          exportedBuffer = audioBufferToWav(buffer, {
+            format: 'wav',
+            bitDepth: settings.bitDepth,
+            normalize: settings.normalize,
+          });
+          mimeType = 'audio/wav';
+          fileExtension = 'wav';
+        }
 
-      if (settings.format === 'mp3') {
-        exportedBuffer = await audioBufferToMp3(mixedBuffer, {
-          format: 'mp3',
-          bitrate: settings.bitrate,
-          normalize: settings.normalize,
+        const fullFilename = `${filename}.${fileExtension}`;
+        downloadArrayBuffer(exportedBuffer, fullFilename, mimeType);
+        return fullFilename;
+      };
+
+      if (settings.scope === 'tracks') {
+        // Export each track individually
+        let exportedCount = 0;
+        for (const track of tracks) {
+          if (!track.audioBuffer) continue;
+
+          const trackFilename = `${settings.filename}_${track.name.replace(/[^a-z0-9]/gi, '_')}`;
+          await convertAndDownload(track.audioBuffer, trackFilename);
+          exportedCount++;
+        }
+
+        addToast({
+          title: 'Export Complete',
+          description: `Exported ${exportedCount} track${exportedCount !== 1 ? 's' : ''}`,
+          variant: 'success',
+          duration: 3000,
         });
-        mimeType = 'audio/mpeg';
-        fileExtension = 'mp3';
-      } else if (settings.format === 'flac') {
-        exportedBuffer = await audioBufferToFlac(mixedBuffer, {
-          format: 'flac',
-          bitDepth: settings.bitDepth,
-          quality: settings.quality,
-          normalize: settings.normalize,
+      } else if (settings.scope === 'selection') {
+        // Export selected region
+        const selectedTrack = tracks.find(t => t.selection);
+        if (!selectedTrack || !selectedTrack.selection) {
+          addToast({
+            title: 'No Selection',
+            description: 'No region selected for export',
+            variant: 'warning',
+            duration: 3000,
+          });
+          setIsExporting(false);
+          return;
+        }
+
+        // Extract selection from all tracks and mix
+        const selectionStart = selectedTrack.selection.start;
+        const selectionEnd = selectedTrack.selection.end;
+        const selectionDuration = selectionEnd - selectionStart;
+
+        // Create tracks with only the selected region
+        const selectedTracks = tracks.map(track => ({
+          ...track,
+          audioBuffer: track.audioBuffer
+            ? extractBufferSegment(track.audioBuffer, selectionStart, selectionEnd)
+            : null,
+        }));
+
+        const mixedBuffer = mixTracks(selectedTracks, sampleRate, selectionDuration);
+        const filename = await convertAndDownload(mixedBuffer, settings.filename);
+
+        addToast({
+          title: 'Export Complete',
+          description: `Exported ${filename}`,
+          variant: 'success',
+          duration: 3000,
         });
-        mimeType = 'application/octet-stream'; // FLAC MIME type
-        fileExtension = 'flac';
       } else {
-        // WAV (default)
-        exportedBuffer = audioBufferToWav(mixedBuffer, {
-          format: 'wav',
-          bitDepth: settings.bitDepth,
-          normalize: settings.normalize,
+        // Export entire project (mix all tracks)
+        const maxDuration = getMaxTrackDuration(tracks);
+        const mixedBuffer = mixTracks(tracks, sampleRate, maxDuration);
+        const filename = await convertAndDownload(mixedBuffer, settings.filename);
+
+        addToast({
+          title: 'Export Complete',
+          description: `Exported ${filename}`,
+          variant: 'success',
+          duration: 3000,
         });
-        mimeType = 'audio/wav';
-        fileExtension = 'wav';
       }
 
-      // Download
-      const filename = `${settings.filename}.${fileExtension}`;
-      downloadArrayBuffer(exportedBuffer, filename, mimeType);
-
-      addToast({
-        title: 'Export Complete',
-        description: `Exported ${filename}`,
-        variant: 'success',
-        duration: 3000,
-      });
-
       setExportDialogOpen(false);
     } catch (error) {
       console.error('Export failed:', error);
@@ -1219,6 +1275,7 @@ export function AudioEditor() {
         onClose={() => setExportDialogOpen(false)}
         onExport={handleExport}
         isExporting={isExporting}
+        hasSelection={tracks.some(t => t.selection !== null)}
       />
     </>
   );