feat: Implement floating feature browser in viewport with transparent background

Co-authored-by: aider (gemini/gemini-2.5-pro) <aider@aider.chat>

src/MainWindow.h

@@ -6,8 +6,6 @@
 class ViewportWidget;
 class Document;
 class Feature;
-class QTreeWidget;
-class QTreeWidgetItem;
 
 class MainWindow : public QMainWindow
 {
@@ -23,18 +21,12 @@ private slots:
     bool saveAs();
     void createSketch();
 
-    void onFeatureAdded(Feature* feature);
-    void onDocumentCleared();
-
 private:
     void setCurrentFile(const QString &fileName);
 
     ViewportWidget *m_viewport;
     Document *m_document;
     QString m_currentFile;
-
-    QTreeWidget* m_featureTree;
-    QTreeWidgetItem* m_rootItem;
 };
 
 #endif // MAINWINDOW_H