feat: Add sketch creation with plane selection, oriented grid and labeled axes

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

src/MainWindow.h

@@ -3,12 +3,20 @@
 
 #include <QMainWindow>
 
+class ViewportWidget;
+
 class MainWindow : public QMainWindow
 {
     Q_OBJECT
 
 public:
     explicit MainWindow(QWidget *parent = nullptr);
+
+private slots:
+    void createSketch();
+
+private:
+    ViewportWidget *m_viewport;
 };
 
 #endif // MAINWINDOW_H