refactor: Move axis label drawing logic from ViewportWidget to SketchGrid

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

src/SketchGrid.h

@@ -7,6 +7,8 @@
 #include <QOpenGLBuffer>
 
 class QOpenGLShaderProgram;
+class QPainter;
+class ViewportWidget;
 
 class SketchGrid : protected QOpenGLFunctions
 {
@@ -17,11 +19,12 @@ public:
         YZ = 3
     };
 
-    SketchGrid();
+    explicit SketchGrid(ViewportWidget* viewport);
     ~SketchGrid();
 
     void initializeGL();
     void paintGL(SketchPlane plane, QOpenGLShaderProgram* shaderProgram, int colorLoc);
+    void paintAxisLabels(QPainter& painter, SketchPlane plane, const QMatrix4x4& modelView, const QMatrix4x4& projection);
 
 private:
     void drawGridLines(SketchPlane plane, QOpenGLShaderProgram* shaderProgram, int colorLoc);
@@ -29,6 +32,7 @@ private:
 
     QOpenGLVertexArrayObject m_vao;
     QOpenGLBuffer m_vbo;
+    ViewportWidget* m_viewport = nullptr;
 };
 
 #endif // SKETCHGRID_H