refactor: remove configurable track height setting

Removed the defaultTrackHeight setting from UI preferences as it doesn't need
to be user-configurable. All tracks now use DEFAULT_TRACK_HEIGHT constant (400px).

Changes:
- Removed defaultTrackHeight from UISettings interface
- Removed track height slider from GlobalSettingsDialog
- Updated AudioEditor to use DEFAULT_TRACK_HEIGHT constant directly
- Simplified dependency arrays in addTrack callbacks

This simplifies the settings interface while maintaining the same visual behavior.

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

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

components/settings/GlobalSettingsDialog.tsx

@@ -400,29 +400,6 @@ export function GlobalSettingsDialog({
                     Adjust the UI font size. Requires reload.
                   </p>
                 </div>
-
-                {/* Default Track Height */}
-                <div className="space-y-2">
-                  <div className="flex items-center justify-between">
-                    <label className="text-sm font-medium">Default Track Height</label>
-                    <span className="text-xs font-mono text-muted-foreground">
-                      {settings.ui.defaultTrackHeight}px
-                    </span>
-                  </div>
-                  <Slider
-                    value={[settings.ui.defaultTrackHeight]}
-                    onValueChange={([value]) =>
-                      onUISettingsChange({ defaultTrackHeight: value })
-                    }
-                    min={120}
-                    max={600}
-                    step={20}
-                    className="w-full"
-                  />
-                  <p className="text-xs text-muted-foreground">
-                    Initial height for new tracks. Default: 400px.
-                  </p>
-                </div>
               </div>
             )}