refactor: Introduce SketchTool base class and derived tool skeletons

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

src/ViewportWidget.h

@@ -20,6 +20,7 @@ class Document;
 class FeatureBrowser;
 class SketchFeature;
 class Camera;
+class SketchTool;
 
 class ViewportWidget : public QOpenGLWidget, protected QOpenGLFunctions
 {
@@ -90,10 +91,8 @@ private:
     SketchPlane m_highlightedPlane = SketchPlane::NONE;
 
     int m_activeTool = 0;
-    bool m_isDefiningLine = false;
-    gp_Pnt m_firstLinePoint;
-    bool m_isDefiningRectangle = false;
-    gp_Pnt m_firstRectanglePoint;
+    SketchTool* m_activeSketchTool = nullptr;
+    QMap<int, SketchTool*> m_sketchTools;
     QPoint m_currentMousePos;
     bool m_isSnappingOrigin = false;
     bool m_isSnappingVertex = false;