feat: Display camera zoom level in viewport

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

src/ViewportWidget.cpp

@@ -180,6 +180,9 @@ void ViewportWidget::paintGL()
         m_activeSketchTool->paint2D(painter, model, projection);
     }
 
+    painter.setPen(Qt::white);
+    painter.drawText(width() - 150, height() - 10, QString("Camera Distance: %1").arg(-m_camera->zoom()));
+
     painter.end();
 }