fix: log etch line failures instead of silently swallowing

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ExportDXF/Services/PartExporter.cs

@@ -234,7 +234,7 @@ namespace ExportDXF.Services
                 var drawingModel = templateDrawing as ModelDoc2;
                 drawingModel.SaveAs(savePath);
 
-                AddEtchLines(savePath);
+                AddEtchLines(savePath, context);
 
                 context.ProgressCallback?.Invoke($"Saved to \"{savePath}\"", LogLevel.Info, partTitle);
 
@@ -301,7 +301,7 @@ namespace ExportDXF.Services
             drawing.DeleteSelection(false);
         }
 
-        private void AddEtchLines(string dxfPath)
+        private void AddEtchLines(string dxfPath, ExportContext context)
         {
             try
             {
@@ -309,9 +309,9 @@ namespace ExportDXF.Services
                 etcher.AddEtchLines(dxfPath);
                 FixDegreeSymbol(dxfPath);
             }
-            catch (Exception)
+            catch (Exception ex)
             {
-                // Silently fail if etch lines can't be added
+                context.ProgressCallback?.Invoke($"Etch lines failed: {ex.Message}", LogLevel.Warning, Path.GetFileName(dxfPath));
             }
         }