Add back navigation from login to setup screen

- Add back button on login page for first-time online mode setup
- Allow users to return to setup screen and change their mode selection
- Add backToSetup localization string for English and German

lib/features/auth/presentation/pages/login_page.dart

@@ -3,6 +3,7 @@ import 'package:go_router/go_router.dart';
 import 'package:provider/provider.dart';
 
 import '../../../../l10n/app_localizations.dart';
+import '../../../settings/presentation/viewmodels/settings_viewmodel.dart';
 import '../viewmodels/auth_viewmodel.dart';
 
 class LoginPage extends StatefulWidget {
@@ -178,6 +179,19 @@ class _LoginPageState extends State<LoginPage> {
                         ),
                       ],
                     ),
+                    const SizedBox(height: 16),
+                    TextButton.icon(
+                      onPressed: () async {
+                        final settingsVm = context.read<SettingsViewModel>();
+                        await settingsVm.setSetupCompleted(false);
+                        await settingsVm.setOnboardingShown(false);
+                        if (context.mounted) {
+                          context.go('/setup');
+                        }
+                      },
+                      icon: const Icon(Icons.arrow_back),
+                      label: Text(l10n.backToSetup),
+                    ),
                   ],
                 ),
               ),

lib/l10n/app_de.arb

@@ -76,5 +76,6 @@
   "switchModeWarning": "Der Moduswechsel ändert, wie Ihre Aufgaben gespeichert werden.",
   "uploadTasksQuestion": "Möchten Sie Ihre lokalen Aufgaben auf den Server hochladen?",
   "yes": "Ja",
-  "no": "Nein"
+  "no": "Nein",
+  "backToSetup": "Zurück zur Einrichtung"
 }

lib/l10n/app_en.arb

@@ -76,5 +76,6 @@
   "switchModeWarning": "Switching modes will change how your tasks are stored.",
   "uploadTasksQuestion": "Would you like to upload your local tasks to the server?",
   "yes": "Yes",
-  "no": "No"
+  "no": "No",
+  "backToSetup": "Back to Setup"
 }

lib/l10n/app_localizations.dart

@@ -559,6 +559,12 @@ abstract class AppLocalizations {
   /// In en, this message translates to:
   /// **'No'**
   String get no;
+
+  /// No description provided for @backToSetup.
+  ///
+  /// In en, this message translates to:
+  /// **'Back to Setup'**
+  String get backToSetup;
 }
 
 class _AppLocalizationsDelegate

lib/l10n/app_localizations_de.dart

@@ -245,4 +245,7 @@ class AppLocalizationsDe extends AppLocalizations {
 
   @override
   String get no => 'Nein';
+
+  @override
+  String get backToSetup => 'Zurück zur Einrichtung';
 }

lib/l10n/app_localizations_en.dart

@@ -243,4 +243,7 @@ class AppLocalizationsEn extends AppLocalizations {
 
   @override
   String get no => 'No';
+
+  @override
+  String get backToSetup => 'Back to Setup';
 }