refactor: Manage active sketch state in ApplicationController

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

src/ApplicationController.h

@@ -6,6 +6,7 @@
 
 class Document;
 class MainWindow;
+class SketchFeature;
 
 class ApplicationController : public QObject
 {
@@ -15,6 +16,7 @@ public:
 
     void setMainWindow(MainWindow* mainWindow);
     Document* document() const;
+    SketchFeature* activeSketch() const;
 
 public slots:
     void newDocument();
@@ -41,6 +43,7 @@ private:
     Document* m_document;
     QString m_currentFile;
     MainWindow* m_mainWindow = nullptr;
+    SketchFeature* m_activeSketch = nullptr;
 };
 
 #endif // APPLICATIONCONTROLLER_H