refactor(#155): option C — widgets partagés sans préfixe Admin.

Déplace les composants Admin* du dashboard partagé vers
widgets/dashboard/ (ChildDetailModal, AmEditModal, UserCard, Select*, …).
Conserve AdminManagementWidget et screens/administrateurs. Rename mécanique,
aucun changement de comportement.

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

frontend/lib/widgets/admin/user_management_panel.dart

@@ -3,8 +3,8 @@ import 'package:p_tits_pas/screens/administrateurs/creation/gestionnaires_create
 import 'package:p_tits_pas/widgets/admin/admin_management_widget.dart';
 import 'package:p_tits_pas/widgets/admin/am_dossier_create_modal.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/dashboard/child_detail_modal.dart';
+import 'package:p_tits_pas/widgets/dashboard/user_management_sub_bar.dart';
 import 'package:p_tits_pas/widgets/admin/dossiers_management_widget.dart';
 import 'package:p_tits_pas/widgets/admin/enfant_management_widget.dart';
 import 'package:p_tits_pas/widgets/admin/gestionnaire_management_widget.dart';
@@ -348,7 +348,7 @@ class _UserManagementPanelState extends State<UserManagementPanel> {
         context: context,
         barrierDismissible: false,
         builder: (dialogContext) {
-          return AdminChildDetailModal.create(
+          return ChildDetailModal.create(
             onSaved: () {
               if (!mounted) return;
               setState(() => _enfantRefreshTick++);