feat(elksharp): A* node proximity cost, increased layer spacing, bridge gap curve awareness, post-pipeline clearance enforcement

Three-layer edge-node clearance improvement:

1. A* proximity cost with correct coordinates: pass original (uninflated)
   node bounds to ComputeNodeProximityCost so the pathfinder penalizes
   edges near real node boundaries, not the inflated obstacle margin.
   Weight=800, clearance=40px. Grid lines added at clearance distance
   from real nodes.

2. Default LayerSpacing increased from 60 to 80, adaptive multiplier
   floor raised from 0.92 to 1.0, giving wider routing corridors
   between node rows.

3. Post-pipeline EnforceMinimumNodeClearance: final unconditional pass
   pushes horizontal segments within 8px of node tops (12px push) or
   within minClearance of node bottoms (full clearance push).

Also: bridge gap detection now uses curve-aware effective segments
(same preprocessing + corner pull-back as BuildRoundedEdgePath) so
gaps only appear at genuine visual crossings. Collector trunks and
same-group edges excluded from gap detection.

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

src/__Libraries/StellaOps.ElkSharp/ElkEdgeRouterIterative.StrategyRepair.RouteAllEdges.cs

@@ -20,6 +20,7 @@ internal static partial class ElkEdgeRouterIterative
             baseObstacleMargin,
             Math.Max(strategy.MinLineClearance + 4d, strategy.RoutingParams.Margin));
         var obstacles = BuildObstacles(nodes, obstacleMargin);
+        var originalNodeBounds = BuildOriginalNodeBounds(nodes);
         var graphMinY = nodes.Length > 0 ? nodes.Min(n => n.Y) : 0d;
         var graphMaxY = nodes.Length > 0 ? nodes.Max(n => n.Y + n.Height) : 0d;
         var nodesById = nodes.ToDictionary(n => n.Id, StringComparer.Ordinal);
@@ -74,6 +75,7 @@ internal static partial class ElkEdgeRouterIterative
                     startPoint,
                     adjustedEndPoint,
                     obstacles,
+                    originalNodeBounds,
                     edge.SourceNodeId ?? "",
                     edge.TargetNodeId ?? "",
                     strategy.RoutingParams,