refactor: Extract snapping logic into dedicated Snapping class

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

src/Snapping.h

@@ -0,0 +1,28 @@
+#ifndef SNAPPING_H
+#define SNAPPING_H
+
+#include <gp_Pnt.hxx>
+#include <QPoint>
+
+class ViewportWidget;
+
+class Snapping
+{
+public:
+    explicit Snapping(ViewportWidget* viewport);
+
+    bool update(const QPoint& mousePos);
+    void paintGL() const;
+
+    bool isSnappingOrigin() const { return m_isSnappingOrigin; }
+    bool isSnappingVertex() const { return m_isSnappingVertex; }
+    const gp_Pnt& snapVertex() const { return m_snapVertex; }
+
+private:
+    ViewportWidget* m_viewport = nullptr;
+    bool m_isSnappingOrigin = false;
+    bool m_isSnappingVertex = false;
+    gp_Pnt m_snapVertex;
+};
+
+#endif // SNAPPING_H