fix(import): compute ellipse minor axis without MinorAxisEndpoint

ACadSharp removed the computed MinorAxisEndpoint property. Derive the
minor axis vector inline using the same formula: Normal × MajorAxis,
normalized, scaled by MajorAxis.Length * RadiusRatio.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ka4ocDhmumPuQDD2fDs7ad

Author: claude

CADability/ImportDxf.cs

@@ -552,7 +552,11 @@ private IGeoObject CreateEllipse(ACadSharp.Entities.Ellipse ellipse)
         {
             GeoObject.Ellipse e = GeoObject.Ellipse.Construct();
             GeoVector majorAxisVec = GeoVector(ellipse.MajorAxisEndPoint);
-            GeoVector minorAxisVec = GeoVector(ellipse.MinorAxisEndpoint);
+            // MinorAxisEndpoint was removed from ACadSharp; compute it from Normal × MajorAxis × RadiusRatio.
+            GeoVector normalVec = GeoVector(ellipse.Normal);
+            GeoVector minorDir = normalVec ^ majorAxisVec;
+            if (!minorDir.IsNullVector()) minorDir.Norm();
+            GeoVector minorAxisVec = minorDir * (majorAxisVec.Length * ellipse.RadiusRatio);
             e.SetEllipseCenterAxis(GeoPoint(ellipse.Center), majorAxisVec, minorAxisVec);
             e.StartParameter = ellipse.StartParameter;
             e.SweepParameter = ellipse.EndParameter - ellipse.StartParameter;