Add reusable two-factor verification for login and money operations (#32)

frontend/app/lib/routing/router.dart

@@ -8,6 +8,7 @@ import 'package:sxchnge_wallet/sxchnge_wallet.dart';
 
 import '../auth/page.dart';
 import '../kyc/page.dart';
+import '../security/challenge.dart';
 import '../verification/page.dart';
 import '../workspace/accounts.dart';
 import '../workspace/activity.dart';
@@ -27,6 +28,16 @@ GoRouter createAppRouter() {
     // Signup email is an in-memory navigation extra, never browser-history data.
     extraCodec: const _TransientExtras(),
     routes: [
+      GoRoute(
+        path: '/two-factor',
+        redirect: (context, state) =>
+            state.extra is FactorRouteRequest ? null : '/',
+        builder: (context, state) =>
+            FactorRoute(request: state.extra as FactorRouteRequest),
+        onExit: (context, state) =>
+            state.extra is! FactorRouteRequest ||
+            !(state.extra as FactorRouteRequest).provider.busy,
+      ),
       ShellRoute(
         builder: (context, state, child) =>
             WorkspaceShell(path: state.uri.path, child: child),