feat: Implement circle drawing tool

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

src/SketchCircle.h

@@ -0,0 +1,26 @@
+#ifndef SKETCHCIRCLE_H
+#define SKETCHCIRCLE_H
+
+#include "SketchObject.h"
+#include <gp_Pnt.hxx>
+
+class SketchCircle : public SketchObject
+{
+public:
+    SketchCircle();
+    SketchCircle(const gp_Pnt& center, double radius);
+
+    ObjectType type() const override;
+
+    void read(const QJsonObject& json) override;
+    void write(QJsonObject& json) const override;
+
+    const gp_Pnt& center() const;
+    double radius() const;
+
+private:
+    gp_Pnt m_center;
+    double m_radius;
+};
+
+#endif // SKETCHCIRCLE_H