fix: parse equipment number from part names without drawing number

Add equipmentOnlyRegex fallback so names like "5028 Prox switch bracket"
correctly extract equipment number 5028 even without a drawing number.
Handle null DrawingNo in ToString and UI dropdown population.

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

ExportDXF/DrawingInfo.cs

@@ -1,10 +1,11 @@
-using System.Text.RegularExpressions;
+using System.Text.RegularExpressions;
 
 namespace ExportDXF
 {
     public class DrawingInfo
     {
         private static Regex drawingFormatRegex = new Regex(@"(?<equipmentNo>[345]\d{3}(-\d+\w{1,2})?)\s?(?<dwgNo>[ABEP]\d+(-?(\d+[A-Z]?))?)", RegexOptions.IgnoreCase);
+        private static Regex equipmentOnlyRegex = new Regex(@"^(?<equipmentNo>[345]\d{3}(-\d+\w{1,2})?)\b", RegexOptions.IgnoreCase);
 
         public string EquipmentNo { get; set; }
 
@@ -14,6 +15,8 @@ namespace ExportDXF
 
         public override string ToString()
         {
+            if (string.IsNullOrEmpty(DrawingNo))
+                return EquipmentNo ?? string.Empty;
             return $"{EquipmentNo} {DrawingNo}";
         }
 
@@ -35,7 +38,21 @@ namespace ExportDXF
             var match = drawingFormatRegex.Match(input);
 
             if (match.Success == false)
+            {
+                // Try matching just the equipment number (e.g. "5028 Prox switch bracket")
+                var eqMatch = equipmentOnlyRegex.Match(input);
+                if (eqMatch.Success)
+                {
+                    return new DrawingInfo
+                    {
+                        EquipmentNo = eqMatch.Groups["equipmentNo"].Value,
+                        DrawingNo = null,
+                        Source = input
+                    };
+                }
+
                 return null;
+            }
 
             var dwg = new DrawingInfo();