fix: Prevent sketch overlap and improve plane selection visibility

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

src/ApplicationController.cpp

@@ -102,6 +102,9 @@ bool ApplicationController::saveDocumentAs()
 
 void ApplicationController::beginSketchCreation()
 {
+    if (m_activeSketch) {
+        return;
+    }
     emit planeSelectionModeStarted();
 }
 

src/ViewportWidget.cpp

@@ -489,6 +489,13 @@ void ViewportWidget::keyPressEvent(QKeyEvent *event)
             update();
             return;
         }
+        if (m_isSelectingPlane) {
+            m_isSelectingPlane = false;
+            m_highlightedPlane = SketchPlane::NONE;
+            m_currentPlane = SketchPlane::XY;
+            update();
+            return;
+        }
     }
     QOpenGLWidget::keyPressEvent(event);
 }
@@ -566,6 +573,7 @@ void ViewportWidget::onPlaneSelectionModeStarted()
 {
     m_isSelectingPlane = true;
     m_highlightedPlane = SketchPlane::NONE;
+    m_currentPlane = SketchPlane::NONE;
     update();
 }