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);

src/Web/StellaOps.Web/src/app/features/topology/topology-graph.component.ts

@@ -106,11 +106,28 @@ import {
                   [attr.marker-end]="selectedEdgeId() === edge.id ? 'url(#arrow-promotion-selected)' : 'url(#arrow-promotion)'"
                 />
                 @if (edge.label) {
+                  <!-- Tooltip callout: dashed leader line + label box offset above edge -->
+                  <line
+                    [attr.x1]="getEdgeLabelX(edge)"
+                    [attr.y1]="getEdgeLabelAnchorY(edge)"
+                    [attr.x2]="getEdgeLabelX(edge)"
+                    [attr.y2]="getEdgeLabelY(edge) + 6"
+                    class="edge-leader"
+                  />
+                  <rect
+                    [attr.x]="getEdgeLabelX(edge) - getEdgeLabelWidth(edge) / 2 - 4"
+                    [attr.y]="getEdgeLabelY(edge) - 6"
+                    [attr.width]="getEdgeLabelWidth(edge) + 8"
+                    height="14"
+                    rx="3"
+                    ry="3"
+                    class="edge-label-bg"
+                  />
                   <text
                     [attr.x]="getEdgeLabelX(edge)"
-                    [attr.y]="getEdgeLabelY(edge)"
+                    [attr.y]="getEdgeLabelY(edge) + 4"
                     class="edge-label"
-                  >{{ edge.label }}</text>
+                  >{{ truncateEdgeLabel(edge.label) }}</text>
                 }
               </g>
             }
@@ -341,8 +358,32 @@ import {
       stroke-width: 2.5;
     }
 
+    .edge-leader {
+      stroke: var(--color-text-muted);
+      stroke-width: 0.5;
+      stroke-dasharray: 2 2;
+      opacity: 0.5;
+      pointer-events: none;
+    }
+
+    .edge-group:hover .edge-leader {
+      opacity: 0.8;
+    }
+
+    .edge-label-bg {
+      fill: var(--color-surface-primary);
+      stroke: var(--color-border-primary);
+      stroke-width: 0.5;
+      opacity: 0.9;
+      pointer-events: none;
+    }
+
+    .edge-group--selected .edge-label-bg {
+      stroke: var(--color-brand-primary);
+    }
+
     .edge-label {
-      font-size: 9px;
+      font-size: 8px;
       fill: var(--color-text-muted);
       text-anchor: middle;
       pointer-events: none;
@@ -553,7 +594,21 @@ export class TopologyGraphComponent {
   }
 
   getEdgeLabelY(edge: TopologyRoutedEdge): number {
-    return this.edgeMidpoint(edge).y - 6;
+    return this.edgeMidpoint(edge).y - 22;
+  }
+
+  getEdgeLabelAnchorY(edge: TopologyRoutedEdge): number {
+    return this.edgeMidpoint(edge).y;
+  }
+
+  getEdgeLabelWidth(edge: TopologyRoutedEdge): number {
+    const label = this.truncateEdgeLabel(edge.label);
+    return label.length * 4.5;
+  }
+
+  truncateEdgeLabel(label: string | undefined | null): string {
+    if (!label) return '';
+    return label.length > 30 ? label.substring(0, 29) + '\u2026' : label;
   }
 
   truncate(text: string | undefined | null, max: number): string {