feat: address missing features and bugs identified during Milestone 3 demo; improve localization, error handling, and navigation

apps/mobile/packages/features/client/billing/lib/billing.dart

@@ -1,4 +1,3 @@
 library;
 
-export 'src/presentation/navigation/billing_navigator.dart';
 export 'src/billing_module.dart';

apps/mobile/packages/features/client/billing/lib/src/presentation/navigation/billing_navigator.dart

@@ -1,7 +0,0 @@
-import 'package:flutter_modular/flutter_modular.dart';
-
-/// Extension on [IModularNavigator] to provide typed navigation for the billing feature.
-extension BillingNavigator on IModularNavigator {
-  /// Navigates to the billing page.
-  void pushBilling() => pushNamed('/billing/');
-}

apps/mobile/packages/features/client/billing/lib/src/presentation/pages/billing_page.dart

@@ -3,6 +3,7 @@ import 'package:design_system/design_system.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:flutter_modular/flutter_modular.dart';
+import 'package:krow_core/core.dart';
 
 import '../blocs/billing_bloc.dart';
 import '../blocs/billing_event.dart';
@@ -83,7 +84,7 @@ class _BillingViewState extends State<BillingView> {
                 leading: Center(
                   child: UiIconButton.secondary(
                     icon: UiIcons.arrowLeft,
-                    onTap: () => Modular.to.navigate('/client-main/home/'),
+                    onTap: () => Modular.to.toClientHome()
                   ),
                 ),
                 title: AnimatedSwitcher(