refactor: Implement Rectangle tool with snapping and dimensions

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

src/SketchFeature.cpp

@@ -1,6 +1,7 @@
 #include "SketchFeature.h"
 #include "SketchObject.h"
 #include "SketchLine.h"
+#include "SketchRectangle.h"
 
 #include <QJsonArray>
 
@@ -66,6 +67,10 @@ void SketchFeature::read(const QJsonObject& json)
                     auto line = new SketchLine();
                     line->read(objectJson);
                     m_objects.append(line);
+                } else if (type == "Rectangle") {
+                    auto rect = new SketchRectangle();
+                    rect->read(objectJson);
+                    m_objects.append(rect);
                 }
             }
         }