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/jest.environment.js

@@ -0,0 +1,22 @@
+/**
+ * Custom Jest environment that extends jest-environment-jsdom and polyfills
+ * the Fetch API (fetch, Request, Response, Headers) from Node 18+'s native
+ * implementation.  This lets tests spy on `global.fetch` with jest.spyOn.
+ */
+const JSDOMEnvironment = require('jest-environment-jsdom').default;
+
+class CustomJSDOMEnvironment extends JSDOMEnvironment {
+  async setup() {
+    await super.setup();
+
+    // Node 18+ exposes fetch on globalThis; copy it into the jsdom sandbox.
+    if (typeof globalThis.fetch === 'function') {
+      this.global.fetch = globalThis.fetch.bind(globalThis);
+      this.global.Request = globalThis.Request;
+      this.global.Response = globalThis.Response;
+      this.global.Headers = globalThis.Headers;
+    }
+  }
+}
+
+module.exports = CustomJSDOMEnvironment;