Add diagonal elimination to hybrid winner refinement

EliminateDiagonalSegments runs in the hybrid baseline finalization but
large diagonals can re-appear during iterative optimization. Added a
conditional elimination pass in the winner refinement when
LongDiagonalViolations > 0.

NodeSpacing=40 retained (default). Tested 42/45/50/60 — each creates
different violations because the routing is tuned for 40. Wider spacing
needs its own tuning pass.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/Workflow/__Tests/StellaOps.Workflow.Renderer.Tests/DocumentProcessingWorkflowRenderingTests.Artifacts.cs

@@ -40,6 +40,7 @@ public partial class DocumentProcessingWorkflowRenderingTests
         var layout = await engine.LayoutAsync(graph, new WorkflowRenderLayoutRequest
         {
             Direction = WorkflowRenderLayoutDirection.LeftToRight,
+            NodeSpacing = 40,
         });
 
         var svgRenderer = new WorkflowRenderSvgRenderer();