feat(frontend): topology compare/Pareto UI

Add a Compare tab to /topologies: pick a task + roles + topology kinds, build a
graph per kind, run POST /api/topologies/compare, and render a leaderboard table
+ a quality/cost Pareto scatter (SVG, no deps). Wrap Build + Compare in a tabbed
TopologyWorkbench. e2e p8 extended to run a comparison end-to-end (build×N →
compare → leaderboard + Pareto). Full suite 39 green; build + TS clean.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

frontend/src/app/(workspace)/topologies/page.tsx

@@ -1,5 +1,5 @@
 import { PageChrome } from "@/components/global/PageChrome";
-import { TopologyExplorer } from "@/components/topology/TopologyExplorer";
+import { TopologyWorkbench } from "@/components/topology/TopologyWorkbench";
 import { fetchTopologyCatalog } from "@/lib/api/topology";
 
 // Topologies page: browse the catalog and build/visualize a topology.
@@ -10,7 +10,7 @@ export default async function TopologiesPage() {
       title="Topologies"
       description={`${catalog.length} organizational patterns to run your agents in`}
     >
-      <TopologyExplorer catalog={catalog} />
+      <TopologyWorkbench catalog={catalog} />
     </PageChrome>
   );
 }