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/__Libraries/StellaOps.ElkSharp/ElkEdgeRouterIterative.BoundaryFirst.TargetJoinReassignment.cs

@@ -83,22 +83,21 @@ internal static partial class ElkEdgeRouterIterative
 
             // Compute the current gap and required spread.
             var currentGap = Math.Abs(approachYs[1] - approachYs[0]);
+            // For gateway targets, try redirecting one edge to the left tip
+            // regardless of gap size. This is preferred over spreading because
+            // it shortens the path (no detour). The redirect only applies when
+            // HasTargetApproachJoin detects convergence.
+            if (ElkShapeBoundaries.IsGatewayShape(targetNode)
+                && ElkEdgeRoutingScoring.HasTargetApproachJoin(
+                    paths[0], paths[1], minClearance, 3))
+            {
+                result = TryRedirectGatewayFaceOverflowEntry(
+                    result, edges, groupEdges, paths, targetNode, approachYs);
+                continue;
+            }
+
             if (currentGap >= minClearance)
             {
-                // Horizontal approach lanes are well separated, but vertical
-                // approach segments near the target may still converge (e.g.,
-                // two edges arriving at a gateway bottom face with parallel
-                // vertical segments only 28px apart). Redirect the edge whose
-                // horizontal approach is closest to the node center to the
-                // upstream face (left tip for LTR).
-                if (ElkShapeBoundaries.IsGatewayShape(targetNode)
-                    && ElkEdgeRoutingScoring.HasTargetApproachJoin(
-                        paths[0], paths[1], minClearance, 3))
-                {
-                    result = TryRedirectGatewayFaceOverflowEntry(
-                        result, edges, groupEdges, paths, targetNode, approachYs);
-                }
-
                 continue;
             }