feat: Implement CircleTool with diameter input and preview

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

src/CircleTool.h

@@ -0,0 +1,28 @@
+#ifndef CIRCLETOOL_H
+#define CIRCLETOOL_H
+
+#include "SketchTool.h"
+#include <gp_Pnt.hxx>
+
+class CircleTool : public SketchTool
+{
+    Q_OBJECT
+public:
+    explicit CircleTool(ViewportWidget* viewport);
+
+    void mousePressEvent(QMouseEvent *event) override;
+    void mouseMoveEvent(QMouseEvent *event) override;
+
+    void paintGL() override;
+    void paint2D(QPainter& painter, const QMatrix4x4& modelView, const QMatrix4x4& projection) override;
+
+    void activate() override;
+
+protected:
+    void finalizeCreation() override;
+
+private:
+    gp_Pnt m_centerPoint;
+};
+
+#endif // CIRCLETOOL_H