fix: prevent multiple ImportDialog instances from appearing

Fixed issue where ImportDialog was being rendered for each track in
waveform mode, causing multiple unclosable dialogs to appear on page load.

Changes:
- Moved ImportDialog to renderControlsOnly mode only
- Each track now has exactly one ImportDialog (rendered in controls column)
- Removed duplicate ImportDialog from renderWaveformOnly mode
- Removed ImportDialog from fallback return statement

This ensures only one dialog appears per track, making it properly closable.

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

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

components/tracks/Track.tsx

@@ -683,6 +683,7 @@ export function Track({
   // Render only controls
   if (renderControlsOnly) {
     return (
+      <>
         <div
           className={cn(
             "w-48 flex-shrink-0 border-b border-r-4 p-2 flex flex-col gap-2 min-h-0 transition-all duration-200 cursor-pointer border-border",
@@ -810,13 +811,23 @@ export function Track({
             </div>
           )}
         </div>
+
+        {/* Import Dialog - Only render in controls mode to avoid duplicates */}
+        <ImportDialog
+          open={showImportDialog}
+          onClose={handleImportCancel}
+          onImport={handleImport}
+          fileName={pendingFile?.name}
+          sampleRate={fileMetadata.sampleRate}
+          channels={fileMetadata.channels}
+        />
+      </>
     );
   }
 
   // Render only waveform
   if (renderWaveformOnly) {
     return (
-      <>
       <div
         className={cn(
           "relative bg-waveform-bg border-b transition-all duration-200",
@@ -900,21 +911,11 @@ export function Track({
           )}
         </div>
       </div>
-
-        {/* Import Dialog */}
-        <ImportDialog
-          open={showImportDialog}
-          onClose={handleImportCancel}
-          onImport={handleImport}
-          fileName={pendingFile?.name}
-          sampleRate={fileMetadata.sampleRate}
-          channels={fileMetadata.channels}
-        />
-      </>
     );
   }
 
   // Render full track (both controls and waveform side by side)
+  // This mode is no longer used - tracks are rendered separately with renderControlsOnly and renderWaveformOnly
   return (
     <div
       ref={containerRef}