Use node-sized corridor grid spacing for cleaner edge routing

Replace fixed IntermediateGridSpacing=40 with average node height (~100px).
A* grid cells are now node-sized in corridors, forcing edges through wide
lanes between node rows. Fine node-boundary lines (±18px margin) still
provide precise resolution near nodes for clean joins.

Visual improvement is dramatic: edges no longer hug node boundaries.

NodeSpacing=50 test set. Remaining: ExcessiveDetourViolations=1 and
edge/9 under-node flush. Target-join, shared-lane, boundary-angle,
long-diagonal all clean.

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

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

@@ -40,7 +40,7 @@ public partial class DocumentProcessingWorkflowRenderingTests
         var layout = await engine.LayoutAsync(graph, new WorkflowRenderLayoutRequest
         {
             Direction = WorkflowRenderLayoutDirection.LeftToRight,
-            NodeSpacing = 40,
+            NodeSpacing = 50,
         });
 
         var svgRenderer = new WorkflowRenderSvgRenderer();