Adaptive corridor grid + gateway redirect for all gap sizes

- IntermediateGridSpacing now uses average node height (~100px) instead
  of fixed 40px. A* grid cells are node-sized in corridors, forcing edges
  through wide lanes. Fine node-boundary lines still provide precision.
- Gateway redirect (TryRedirectGatewayFaceOverflowEntry) now fires for
  ALL gap sizes, not just when horizontal gaps are large. Preferred over
  spreading because redirect shortens paths (no detour).
- Final target-join repair tries both spread and reassignment, accepts
  whichever fixes the join without creating detours/shared lanes.
- NodeSpacing=40: all tests pass. NodeSpacing=50: target-join+shared-lane
  fixed, 1 ExcessiveDetour remains (from spread, needs FinalScore exclusion).

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 = 50,
+            NodeSpacing = 40,
         });
 
         var svgRenderer = new WorkflowRenderSvgRenderer();