feat: add BomItem and LogEvent models

Added BomItem model with sheet metal properties (thickness, k-factor, bend radius) and LogEvent model for structured logging with action tracking.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

ExportDXF/Models/BomItem.cs

@@ -0,0 +1,32 @@
+using System;
+
+namespace ExportDXF.Models
+{
+    public class BomItem
+    {
+        public int ID { get; set; }
+        public string ItemNo { get; set; } = "";
+        public string PartNo { get; set; } = "";
+        public int SortOrder { get; set; }
+        public int? Qty { get; set; }
+        public int? TotalQty { get; set; }
+        public string Description { get; set; } = "";
+        public string PartName { get; set; } = "";
+        public string ConfigurationName { get; set; } = "";
+        public string Material { get; set; } = "";
+        public int DrawingID { get; set; }
+        public int? CutTemplateID { get; set; }
+        public string CutTemplateName { get; set; } = "";
+
+        // Sheet metal properties from CutTemplate
+        public double? Thickness { get; set; }
+        public double? KFactor { get; set; }
+        public double? DefaultBendRadius { get; set; }
+    }
+
+    public struct Size
+    {
+        public double Width { get; set; }
+        public double Height { get; set; }
+    }
+}