feat(tools): headless DXF+workbook job verification tool

NestDxfJob imports a DXF folder plus a quantity workbook, runs a
registered whole-job engine, and only publishes a nest that passes
quantity, bounds, overlap/spacing, and cut-only checks both before and
after save/reload. Writes import and validation reports; partial or
invalid results exit nonzero. Standalone project (not in the solution);
documented in the README.

tools/NestDxfJob/NestDxfJob.csproj

@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+  <ItemGroup>
+    <ProjectReference Include="../../OpenNest.Benchmark/OpenNest.Benchmark.csproj" />
+  </ItemGroup>
+</Project>