feat: auto-populate title from part description when opening documents

Adds a Description property to DrawingInfo that extracts the
descriptive text after the equipment/drawing number, excluding the
file extension. MainForm now sets the title box from this description
when no title was already set by the API history lookup.

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

ExportDXF/DrawingInfo.cs

@@ -1,3 +1,4 @@
+using System.IO;
 using System.Text.RegularExpressions;
 
 namespace ExportDXF
@@ -13,6 +14,35 @@ namespace ExportDXF
 
         public string Source { get; set; }
 
+        /// <summary>
+        /// The descriptive text after the equipment/drawing number (e.g. "Prox switch bracket for drive").
+        /// </summary>
+        public string Description
+        {
+            get
+            {
+                if (string.IsNullOrEmpty(Source) || string.IsNullOrEmpty(EquipmentNo))
+                    return null;
+
+                // Strip equipment number (and optional drawing number) from the source to get the description
+                var prefix = string.IsNullOrEmpty(DrawingNo)
+                    ? EquipmentNo
+                    : EquipmentNo + " " + DrawingNo;
+
+                var desc = Source;
+                if (desc.StartsWith(prefix, System.StringComparison.OrdinalIgnoreCase))
+                    desc = desc.Substring(prefix.Length);
+
+                // Remove file extension (e.g. ".SLDPRT")
+                var ext = Path.GetExtension(desc);
+                if (!string.IsNullOrEmpty(ext))
+                    desc = desc.Substring(0, desc.Length - ext.Length);
+
+                desc = desc.Trim();
+                return string.IsNullOrEmpty(desc) ? null : desc;
+            }
+        }
+
         public override string ToString()
         {
             if (string.IsNullOrEmpty(DrawingNo))

ExportDXF/Forms/MainForm.cs

@@ -487,6 +487,9 @@ namespace ExportDXF.Forms
                     equipmentBox.Text = drawingInfo.EquipmentNo;
                 }
 
+                if (string.IsNullOrEmpty(titleBox.Text) && !string.IsNullOrEmpty(drawingInfo.Description))
+                    titleBox.Text = drawingInfo.Description;
+
                 // Load drawings for the selected equipment, then set drawing number
                 await UpdateDrawingDropdownAsync();