Merge develop into master (squash): ticket #102 NIR harmonisation

- Backend: DTO NIR 15 car 2A/2B, validation format+clé, warning cohérence
- BDD: nir_chiffre NOT NULL, migration pour bases existantes
- Seeds: 02 nir_chiffre, 03 Marie 2A / Fatima 99
- Frontend: nir_utils, nir_text_field, formulaire pro, mock inscription AM

Made-with: Cursor

frontend/lib/screens/auth/am_register_step2_screen.dart

@@ -54,15 +54,15 @@ class _AmRegisterStep2ScreenState extends State<AmRegisterStep2Screen> {
       capacity: registrationData.capacity,
     );
 
-    // Générer des données de test si les champs sont vides
+    // Générer des données de test si les champs sont vides (NIR = Marie Dubois du seed, Corse 2A)
     if (registrationData.dateOfBirth == null && registrationData.nir.isEmpty) {
       initialData = ProfessionalInfoData(
         photoPath: 'assets/images/icon_assmat.png',
         photoConsent: true,
-        dateOfBirth: DateTime(1985, 3, 15),
-        birthCity: DataGenerator.city(),
+        dateOfBirth: DateTime(1980, 6, 8),
+        birthCity: 'Ajaccio',
         birthCountry: 'France',
-        nir: '${DataGenerator.randomIntInRange(1, 3)}${DataGenerator.randomIntInRange(80, 96)}${DataGenerator.randomIntInRange(1, 13).toString().padLeft(2, '0')}${DataGenerator.randomIntInRange(1, 100).toString().padLeft(2, '0')}${DataGenerator.randomIntInRange(100, 1000).toString().padLeft(3, '0')}${DataGenerator.randomIntInRange(100, 1000).toString().padLeft(3, '0')}${DataGenerator.randomIntInRange(10, 100).toString().padLeft(2, '0')}',
+        nir: '280062A00100191',
         agrementNumber: 'AM${DataGenerator.randomIntInRange(10000, 100000)}',
         capacity: DataGenerator.randomIntInRange(1, 5),
       );