Keep highlight markers filled in wireframe mode

glPolygonMode(GL_LINE) for wireframe applied to the sphere-impostor point
quads too, drawing them as outlines. Reset to GL_FILL after the scene mesh so
wireframe affects only the geometry; highlight points/edges stay filled.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CityDoctorParent/Extensions/CityDoctorGUI/src/main/java/de/hft/stuttgart/citydoctor2/gui/gl/GLViewport.java

@@ -196,6 +196,8 @@ public class GLViewport {
         sceneProgram.use(gl);
         gl.glUniformMatrix4fv(sceneProgram.uniform(gl, "uMVP"), 1, false, mvp, 0);
         scene.draw(gl);
+        // wireframe applies to the geometry only; highlight markers always render filled
+        gl.glPolygonMode(GL.GL_FRONT_AND_BACK, GL3.GL_FILL);
         // edge markers reuse the flat scene program (pos + colour)
         overlay.drawLines(gl, lineScale);
         // vertex markers use the sphere-impostor program (geometry shader -> camera-facing quads)