fix: Disable GL depth and cull face for 2D icon rendering

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

src/ViewportWidget.cpp

@@ -148,6 +148,9 @@ void ViewportWidget::paintGL()
 
     glViewport(0, 0, width(), height());
 
+    glDisable(GL_DEPTH_TEST);
+    glDisable(GL_CULL_FACE);
+
     QPainter painter(this);
     if (m_currentPlane != SketchPlane::NONE) {
         drawAxisLabels(painter, model, projection);