feat: Implement sketch object base class and line geometry

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

src/SketchLine.cpp

@@ -0,0 +1,58 @@
+#include "SketchLine.h"
+#include <QJsonObject>
+
+SketchLine::SketchLine()
+{
+}
+
+SketchLine::SketchLine(const gp_Pnt& start, const gp_Pnt& end)
+    : m_start(start), m_end(end)
+{
+}
+
+SketchObject::ObjectType SketchLine::type() const
+{
+    return ObjectType::Line;
+}
+
+void SketchLine::read(const QJsonObject& json)
+{
+    if (json.contains("start") && json["start"].isObject() &&
+        json.contains("end") && json["end"].isObject()) {
+        QJsonObject startObj = json["start"].toObject();
+        QJsonObject endObj = json["end"].toObject();
+        m_start.SetX(startObj["x"].toDouble());
+        m_start.SetY(startObj["y"].toDouble());
+        m_start.SetZ(startObj["z"].toDouble());
+        m_end.SetX(endObj["x"].toDouble());
+        m_end.SetY(endObj["y"].toDouble());
+        m_end.SetZ(endObj["z"].toDouble());
+    }
+}
+
+void SketchLine::write(QJsonObject& json) const
+{
+    QJsonObject startObj;
+    startObj["x"] = m_start.X();
+    startObj["y"] = m_start.Y();
+    startObj["z"] = m_start.Z();
+
+    QJsonObject endObj;
+    endObj["x"] = m_end.X();
+    endObj["y"] = m_end.Y();
+    endObj["z"] = m_end.Z();
+
+    json["type"] = "Line";
+    json["start"] = startObj;
+    json["end"] = endObj;
+}
+
+const gp_Pnt& SketchLine::startPoint() const
+{
+    return m_start;
+}
+
+const gp_Pnt& SketchLine::endPoint() const
+{
+    return m_end;
+}