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/enfant_management_widget.dart

@@ -5,8 +5,8 @@ import 'package:p_tits_pas/models/enfant_admin_model.dart';
 import 'package:p_tits_pas/services/auth_service.dart';
 import 'package:p_tits_pas/services/user_service.dart';
 import 'package:p_tits_pas/utils/staff_deletion_rights.dart';
-import 'package:p_tits_pas/widgets/admin/common/admin_child_detail_modal.dart';
-import 'package:p_tits_pas/widgets/admin/common/admin_enfant_user_card.dart';
+import 'package:p_tits_pas/widgets/dashboard/child_detail_modal.dart';
+import 'package:p_tits_pas/widgets/dashboard/enfant_user_card.dart';
 import 'package:p_tits_pas/widgets/admin/common/suppression_confirm_dialog.dart';
 import 'package:p_tits_pas/widgets/admin/common/user_list.dart';
 
@@ -68,7 +68,7 @@ class _EnfantManagementWidgetState extends State<EnfantManagementWidget> {
   Future<void> _openEnfant(EnfantAdminModel enfant) async {
     await showDialog<void>(
       context: context,
-      builder: (ctx) => AdminChildDetailModal(
+      builder: (ctx) => ChildDetailModal(
         enfant: enfant,
         onSaved: _loadEnfants,
         onDeleted: _loadEnfants,
@@ -224,7 +224,7 @@ class _EnfantManagementWidgetState extends State<EnfantManagementWidget> {
       itemCount: filtered.length,
       itemBuilder: (context, index) {
         final enfant = filtered[index];
-        return AdminEnfantUserCard.fromEnfant(
+        return EnfantUserCard.fromEnfant(
           enfant,
           onCardTap: () => _openEnfant(enfant),
           actions: [