feat: Add sketch creation with plane selection, oriented grid and labeled axes

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

src/SketchGrid.h

@@ -0,0 +1,27 @@
+#ifndef SKETCHGRID_H
+#define SKETCHGRID_H
+
+#include <QOpenGLFunctions>
+#include <QMatrix4x4>
+
+class SketchGrid : protected QOpenGLFunctions
+{
+public:
+    enum SketchPlane {
+        XY = 1,
+        XZ = 2,
+        YZ = 3
+    };
+
+    SketchGrid();
+    ~SketchGrid();
+
+    void initializeGL();
+    void paintGL(SketchPlane plane, const QMatrix4x4& projection, const QMatrix4x4& modelview);
+
+private:
+    void drawGridLines(SketchPlane plane);
+    void drawAxes(SketchPlane plane);
+};
+
+#endif // SKETCHGRID_H