feat(inscription): email accusé réception, photos enfants, formulaires identité

- Backend: mail après inscription parent avec n° dossier, UPLOAD_PHOTOS_DIR, réponse API
- Frontend: imageBytes + payload photo, utils email/code postal/téléphone, champs dédiés
- Formulaires admin, login (focus), personal_info, child_card, custom_app_text_field

Made-with: Cursor

frontend/lib/screens/auth/parent_register_step3_screen.dart

@@ -3,6 +3,7 @@ import 'package:google_fonts/google_fonts.dart';
 import 'dart:math' as math; // Pour la rotation du chevron
 import 'package:image_picker/image_picker.dart';
 import 'dart:io' show File;
+import 'package:flutter/foundation.dart' show kIsWeb;
 import '../../widgets/hover_relief_widget.dart';
 import '../../widgets/child_card_widget.dart';
 import '../../widgets/custom_navigation_button.dart';
@@ -152,10 +153,19 @@ class _ParentRegisterStep3ScreenState extends State<ParentRegisterStep3Screen> {
       if (pickedFile != null) {
         if (childIndex < registrationData.children.length) {
           final oldChild = registrationData.children[childIndex];
-          final updatedChild = oldChild.copyWith(imageFile: File(pickedFile.path));
+          final bytes = await pickedFile.readAsBytes();
+          if (bytes.isEmpty) return;
+          File? file;
+          if (!kIsWeb) {
+            try {
+              final f = File(pickedFile.path);
+              if (await f.exists()) file = f;
+            } catch (_) {}
+          }
+          final updatedChild = oldChild.copyWith(imageBytes: bytes, imageFile: file);
           registrationData.updateChild(childIndex, updatedChild);
         }
-      } 
+      }
     } catch (e) { print("Erreur image: $e"); }
   }
 
@@ -285,13 +295,14 @@ class _ParentRegisterStep3ScreenState extends State<ParentRegisterStep3Screen> {
                 // Générer les cartes enfants
                 for (int index = 0; index < registrationData.children.length; index++) ...[
                   ChildCardWidget(
-                    key: ValueKey(registrationData.children[index].hashCode),
+                    key: ValueKey('parent_register_child_$index'),
                     childData: registrationData.children[index],
                     childIndex: index,
                     onPickImage: () => _pickImage(index, registrationData),
                     onClearImage: () => setState(() {
                       final c = registrationData.children[index];
-                      registrationData.updateChild(index, c.copyWith(imageFile: null));
+                      registrationData.updateChild(
+                          index, c.copyWith(imageFile: null, imageBytes: null));
                     }),
                     onDateSelect: () => _selectDate(context, index, registrationData),
                     onFirstNameChanged: (value) => setState(() {
@@ -392,13 +403,14 @@ class _ParentRegisterStep3ScreenState extends State<ParentRegisterStep3Screen> {
                               return Padding(
                                 padding: const EdgeInsets.only(right: 20.0),
                                 child: ChildCardWidget(
-                                  key: ValueKey(registrationData.children[index].hashCode), // Utiliser une clé basée sur les données
+                                  key: ValueKey('parent_register_child_$index'),
                                   childData: registrationData.children[index],
                                   childIndex: index,
                                   onPickImage: () => _pickImage(index, registrationData),
                                   onClearImage: () => setState(() {
                                     final c = registrationData.children[index];
-                                    registrationData.updateChild(index, c.copyWith(imageFile: null));
+                                    registrationData.updateChild(
+                                        index, c.copyWith(imageFile: null, imageBytes: null));
                                   }),
                                   onDateSelect: () => _selectDate(context, index, registrationData),
                                   onFirstNameChanged: (value) => setState(() {