refactor: make track control panel full height and remove redundant buttons

Changes:
- Track control panel now uses flexbox (full height, no scrolling)
- Removed "Add Empty Track" and "Import Audio Files" buttons from main area
- All track management is now done via the sidebar only
- Cleaner, more professional DAW-style interface

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

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

components/tracks/Track.tsx

@@ -171,7 +171,7 @@ export function Track({
     >
       {/* Left: Track Control Panel (Fixed Width) */}
       <div
-        className="w-72 flex-shrink-0 bg-card border-r border-border p-3 space-y-2 overflow-y-auto"
+        className="w-72 flex-shrink-0 bg-card border-r border-border p-3 flex flex-col gap-2"
         onClick={(e) => e.stopPropagation()}
       >
         {/* Track Name & Collapse Toggle */}

components/tracks/TrackList.tsx

@@ -108,25 +108,6 @@ export function TrackList({
         ))}
       </div>
 
-      {/* Add Track Buttons */}
-      <div className="p-2 border-t border-border bg-card space-y-2">
-        <Button onClick={onAddTrack} variant="outline" size="sm" className="w-full">
-          <Plus className="h-4 w-4 mr-2" />
-          Add Empty Track
-        </Button>
-        {onImportTrack && (
-          <Button
-            onClick={() => setImportDialogOpen(true)}
-            variant="outline"
-            size="sm"
-            className="w-full"
-          >
-            <Upload className="h-4 w-4 mr-2" />
-            Import Audio Files
-          </Button>
-        )}
-      </div>
-
       {/* Import Dialog */}
       {onImportTrack && (
         <ImportTrackDialog