feat: Implement floating feature browser in viewport with transparent background

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

src/ViewportWidget.h

@@ -10,6 +10,8 @@
 
 class ViewCube;
 class SketchGrid;
+class Document;
+class Feature;
 
 class ViewportWidget : public QOpenGLWidget, protected QOpenGLFunctions
 {
@@ -27,6 +29,7 @@ public:
     ~ViewportWidget();
 
     void startSketch(SketchPlane plane);
+    void setDocument(Document* document);
 
 protected:
     void initializeGL() override;
@@ -40,10 +43,12 @@ protected:
 private:
     QVector3D project(const QVector3D& worldCoord, const QMatrix4x4& modelView, const QMatrix4x4& projection, const QRect& viewport);
     void drawAxisLabels(QPainter& painter, const QMatrix4x4& modelView, const QMatrix4x4& projection);
+    void drawFeatureBrowser(QPainter& painter);
 
     QMatrix4x4 projection;
     ViewCube* m_viewCube;
     SketchGrid* m_sketchGrid = nullptr;
+    Document* m_document = nullptr;
     SketchPlane m_currentPlane = SketchPlane::NONE;
 
     float xRot = 0;