Integrate email notifications into signup and login (#38)

frontend/app/lib/routing/router.dart

@@ -19,12 +19,23 @@ import '../workspace/shell.dart';
 import '../workspace/transfer.dart';
 import 'routes.dart';
 
-GoRouter createAppRouter() {
+GoRouter createAppRouter({bool Function()? authenticated}) {
   final topUpKey = GlobalKey<TransferPageState>();
   final exchangeKey = GlobalKey<TransferPageState>();
   final payoutKey = GlobalKey<TransferPageState>();
   final identityKey = GlobalKey<IdentityPageState>();
   return GoRouter(
+    redirect: (context, state) {
+      if (authenticated == null || authenticated()) return null;
+      final path = state.uri.path;
+      if (path == '/' ||
+          path == '/verify-email' ||
+          path == '/verification-sent' ||
+          path == '/two-factor') {
+        return null;
+      }
+      return '/';
+    },
     // Signup email is an in-memory navigation extra, never browser-history data.
     extraCodec: const _TransientExtras(),
     routes: [