fix(#112): dates et places AM en reprise (resetForReprise)

Corrige l’ombre des paramètres dateOfBirth, agreementDate et placesAvailable
dans resetForReprise ; renforce le parsing reprise-dossier et ajoute un test.

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

frontend/lib/models/am_registration_data.dart

@@ -141,14 +141,14 @@ class AmRegistrationData extends ChangeNotifier {
     photoBytes = null;
     photoFilename = null;
     photoConsent = consentementPhoto;
-    dateOfBirth = dateOfBirth;
+    this.dateOfBirth = dateOfBirth;
     this.birthCity = birthCity;
     this.birthCountry = birthCountry;
     this.nir = nir;
     this.agrementNumber = agrementNumber;
-    agreementDate = agreementDate;
+    this.agreementDate = agreementDate;
     this.capacity = capacity;
-    placesAvailable = placesAvailable;
+    this.placesAvailable = placesAvailable;
     this.presentationText = presentationText;
     cguAccepted = false;
     notifyListeners();