refactor: Introduce SketchTool base class and derived tool skeletons

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

src/SketchTool.h

@@ -0,0 +1,34 @@
+#ifndef SKETCHTOOL_H
+#define SKETCHTOOL_H
+
+#include <QObject>
+
+class QMouseEvent;
+class QKeyEvent;
+class ViewportWidget;
+class QOpenGLShaderProgram;
+class QPainter;
+class QMatrix4x4;
+
+class SketchTool : public QObject
+{
+    Q_OBJECT
+public:
+    explicit SketchTool(ViewportWidget* viewport);
+    virtual ~SketchTool() = default;
+
+    virtual void mousePressEvent(QMouseEvent *event) = 0;
+    virtual void mouseMoveEvent(QMouseEvent *event) = 0;
+    virtual void keyPressEvent(QKeyEvent *event) = 0;
+
+    virtual void paintGL() = 0;
+    virtual void paint2D(QPainter& painter, const QMatrix4x4& modelView, const QMatrix4x4& projection) = 0;
+
+    virtual void activate();
+    virtual void deactivate();
+
+protected:
+    ViewportWidget* m_viewport;
+};
+
+#endif // SKETCHTOOL_H