feat: add revision tracking to CutTemplate and scope BOM items to export record

Each export record now keeps a complete BOM snapshot instead of moving
BomItems between records. CutTemplate gains a Revision field that
auto-increments when the content hash changes across exports for the
same drawing+item, and stays the same when the geometry is unchanged.

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

FabWorks.Core/Models/CutTemplate.cs

@@ -16,6 +16,8 @@ namespace FabWorks.Core.Models
             set => _thickness = value.HasValue ? Math.Round(value.Value, 8) : null;
         }
 
+        public int Revision { get; set; } = 1;
+
         public double? KFactor { get; set; }
 
         private double? _defaultBendRadius;