feat(#132): création enfant admin — modale + sélection famille.

Onglet Enfants « Ajouter » ouvre la fiche en mode création ; bloc Famille/dossier ; client POST /enfants avec parent_user_id (contrat back à livrer).

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

frontend/lib/widgets/admin/user_management_panel.dart

@@ -3,6 +3,7 @@ import 'package:p_tits_pas/screens/administrateurs/creation/gestionnaires_create
 import 'package:p_tits_pas/services/user_service.dart';
 import 'package:p_tits_pas/widgets/admin/admin_management_widget.dart';
 import 'package:p_tits_pas/widgets/admin/assistante_maternelle_management_widget.dart';
+import 'package:p_tits_pas/widgets/admin/common/admin_child_detail_modal.dart';
 import 'package:p_tits_pas/widgets/admin/dashboard_admin.dart';
 import 'package:p_tits_pas/widgets/admin/enfant_management_widget.dart';
 import 'package:p_tits_pas/widgets/admin/gestionnaire_management_widget.dart';
@@ -26,6 +27,7 @@ class _UserManagementPanelState extends State<UserManagementPanel> {
   int _subIndex = 0;
   int _gestionnaireRefreshTick = 0;
   int _adminRefreshTick = 0;
+  int _enfantRefreshTick = 0;
   final TextEditingController _searchController = TextEditingController();
   final TextEditingController _amCapacityController = TextEditingController();
   String? _parentStatus;
@@ -264,6 +266,7 @@ class _UserManagementPanelState extends State<UserManagementPanel> {
         );
       case 1:
         return EnfantManagementWidget(
+          key: ValueKey('enfants-$_enfantRefreshTick'),
           searchQuery: _searchController.text,
           statusFilter: _enfantStatus,
         );
@@ -311,6 +314,23 @@ class _UserManagementPanelState extends State<UserManagementPanel> {
 
   Future<void> _handleAddPressed() async {
     final contentIndex = _subIndex - _contentIndexOffset;
+
+    if (contentIndex == 1) {
+      await showDialog<void>(
+        context: context,
+        barrierDismissible: false,
+        builder: (dialogContext) {
+          return AdminChildDetailModal.create(
+            onSaved: () {
+              if (!mounted) return;
+              setState(() => _enfantRefreshTick++);
+            },
+          );
+        },
+      );
+      return;
+    }
+
     if (contentIndex == 3) {
       final created = await showDialog<bool>(
         context: context,