Improve topology layout spacing and edge label readability

- Increase LayerSpacing from 60 to 120 and NodeSpacing from 40 to 60
  for wider promotion arrows between environments
- Increase CompoundPadding from 30 to 40 for better region container
  separation
- Replace inline edge labels with tooltip callout pattern: truncated
  text in a background box with dashed leader line to the edge
- Edge labels capped at 30 chars with ellipsis

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

src/Platform/StellaOps.Platform.WebService/Services/TopologyLayoutService.cs

@@ -143,8 +143,10 @@ public sealed class TopologyLayoutService
             new ElkLayoutOptions
             {
                 Direction = direction,
-                NodeSpacing = 40,
-                LayerSpacing = 60,
+                NodeSpacing = 60,
+                LayerSpacing = 120,
+                CompoundPadding = 40,
+                CompoundHeaderHeight = 32,
                 Effort = effort,
             },
             cancellationToken).ConfigureAwait(false);