feat(#112): reprise après refus via lien e-mail (/reprise?token=)

Branche le flux front : chargement du dossier, session reprise, wizards
parent/AM préremplis et resoumission via reprise-resoumettre.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/lib/screens/auth/am_register_step1_screen.dart

@@ -4,6 +4,7 @@ import 'package:go_router/go_router.dart';
 
 import '../../models/am_registration_data.dart';
 import '../../widgets/personal_info_form_screen.dart';
+import '../../services/reprise_session.dart';
 import '../../models/card_assets.dart';
 
 class AmRegisterStep1Screen extends StatelessWidget {
@@ -29,7 +30,7 @@ class AmRegisterStep1Screen extends StatelessWidget {
       cardColor: CardColorHorizontal.blue,
       initialData: initialData,
       minPersonNameLength: 2,
-      previousRoute: '/register-choice',
+      previousRoute: RepriseSession.isActive ? '/login' : '/register-choice',
       onSubmit: (data, {hasSecondPerson, sameAddress}) {
         registrationData.updateIdentityInfo(
           firstName: data.firstName,