Fix region rect intercepting edge clicks in SVG topology

Region container rects were blocking pointer events on edges behind
them. Set pointer-events: none on .region-rect so clicks pass through
to the edges layer beneath.

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

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

@@ -318,6 +318,7 @@ import {
       stroke-dasharray: 6 3;
       opacity: 0.7;
       transition: opacity 150ms ease;
+      pointer-events: none;
     }
 
     .region-group:hover .region-rect {