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/Migrations/20260219134027_AddCutTemplateRevision.cs

@@ -0,0 +1,29 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace FabWorks.Core.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddCutTemplateRevision : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AddColumn<int>(
+                name: "Revision",
+                table: "CutTemplates",
+                type: "int",
+                nullable: false,
+                defaultValue: 0);
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropColumn(
+                name: "Revision",
+                table: "CutTemplates");
+        }
+    }
+}