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/api/routes/[id]/route.ts

@@ -0,0 +1,10 @@
+const API_URL = process.env.API_URL ?? 'http://localhost:3001';
+
+export async function DELETE(
+  _req: Request,
+  { params }: { params: Promise<{ id: string }> },
+) {
+  const { id } = await params;
+  const res = await fetch(`${API_URL}/routes/${id}`, { method: 'DELETE' });
+  return new Response(null, { status: res.status });
+}