feat: add Title, EquipmentNo, DrawingNo to ExportRecord

Add separate EquipmentNo and DrawingNo fields alongside the combined
DrawingNumber, plus a Title field for labeling exports. Updated across
Core model, DbContext, API DTOs, and ExportDXF models.

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

ExportDXF/Models/ExportContext.cs

@@ -42,6 +42,11 @@ namespace ExportDXF.Services
         /// </summary>
         public string DrawingNo { get; set; }
 
+        /// <summary>
+        /// Optional title/label for the export.
+        /// </summary>
+        public string Title { get; set; }
+
         /// <summary>
         /// Selected Equipment ID for API operations (optional).
         /// </summary>

ExportDXF/Models/ExportRecord.cs

@@ -7,6 +7,8 @@ namespace ExportDXF.Models
     {
         public int Id { get; set; }
         public string DrawingNumber { get; set; }
+        public string EquipmentNo { get; set; }
+        public string DrawingNo { get; set; }
         public string SourceFilePath { get; set; }
         public string OutputFolder { get; set; }
         public DateTime ExportedAt { get; set; }