feat(web): add groups page with RouteManager and route handler proxies

Implements the Groups & Routes admin page with a client-side RouteManager
component (add/delete sync routes via fetch), server-side groups page that
pre-fetches groups/routes from the API, and Next.js Route Handler proxies
for /api/routes (GET, POST) and /api/routes/[id] (DELETE). Adds a custom
jest environment that polyfills Node 18+ native fetch into the jsdom sandbox
so tests can use jest.spyOn(global, 'fetch').

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/web/app/groups/page.tsx

@@ -0,0 +1,40 @@
+import { RouteManager } from './RouteManager';
+
+interface Group {
+  id: string;
+  name: string;
+  platform: string;
+}
+
+interface Route {
+  id: string;
+  sourceGroupId: string;
+  targetGroupId: string;
+  sourceGroup: { name: string };
+  targetGroup: { name: string };
+}
+
+async function fetchJson<T>(url: string): Promise<T | null> {
+  try {
+    const res = await fetch(url, { cache: 'no-store' });
+    if (!res.ok) return null;
+    return res.json();
+  } catch {
+    return null;
+  }
+}
+
+export default async function GroupsPage() {
+  const apiUrl = process.env.API_URL ?? 'http://localhost:3001';
+  const [groups, routes] = await Promise.all([
+    fetchJson<Group[]>(`${apiUrl}/groups`),
+    fetchJson<Route[]>(`${apiUrl}/routes`),
+  ]);
+
+  return (
+    <div className="max-w-2xl">
+      <h1 className="text-xl font-semibold mb-6">Groups &amp; Routes</h1>
+      <RouteManager groups={groups ?? []} initialRoutes={routes ?? []} />
+    </div>
+  );
+}