feat(#146): modale de sélection d'enfant pour rattachement AM/parent.

Recherche dynamique, filtre Sans garde côté AM, confirmation de transfert et détachement préalable pour laisser le point de vigilance places sur l'AM d'origine.

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

frontend/lib/widgets/admin/common/admin_parent_edit_modal.dart

@@ -1,5 +1,4 @@
 import 'package:flutter/material.dart';
-import 'package:p_tits_pas/models/enfant_admin_model.dart';
 import 'package:p_tits_pas/utils/phone_utils.dart';
 import 'package:p_tits_pas/models/parent_child_summary.dart';
 import 'package:p_tits_pas/models/parent_model.dart';
@@ -7,6 +6,7 @@ import 'package:p_tits_pas/models/user.dart';
 import 'package:p_tits_pas/services/user_service.dart';
 import 'package:p_tits_pas/widgets/admin/common/admin_child_detail_modal.dart';
 import 'package:p_tits_pas/widgets/admin/common/admin_children_affiliation_panel.dart';
+import 'package:p_tits_pas/widgets/admin/common/admin_select_enfant_modal.dart';
 import 'package:p_tits_pas/widgets/admin/common/admin_status_capsule.dart';
 import 'package:p_tits_pas/widgets/common/identity_block.dart';
 import 'package:p_tits_pas/widgets/admin/validation_modal_theme.dart';
@@ -321,41 +321,11 @@ class _AdminParentEditModalState extends State<AdminParentEditModal> {
   }
 
   Future<void> _attachChild() async {
-    List<EnfantAdminModel> all;
-    try {
-      all = await UserService.getEnfants();
-    } catch (e) {
-      if (!mounted) return;
-      ScaffoldMessenger.of(context).showSnackBar(
-        SnackBar(content: Text(e.toString().replaceFirst('Exception: ', ''))),
-      );
-      return;
-    }
-
-    final linkedIds = _children.map((c) => c.id).toSet();
-    final candidates = all.where((e) => !linkedIds.contains(e.id)).toList();
-    if (candidates.isEmpty) {
-      if (!mounted) return;
-      ScaffoldMessenger.of(context).showSnackBar(
-        const SnackBar(content: Text('Aucun enfant disponible à rattacher')),
-      );
-      return;
-    }
-
     if (!mounted) return;
-    final selected = await showDialog<EnfantAdminModel>(
-      context: context,
-      builder: (ctx) => SimpleDialog(
-        title: const Text('Rattacher un enfant'),
-        children: candidates
-            .map(
-              (e) => SimpleDialogOption(
-                onPressed: () => Navigator.pop(ctx, e),
-                child: Text(e.fullName),
-              ),
-            )
-            .toList(),
-      ),
+    final selected = await AdminSelectEnfantModal.show(
+      context,
+      excludeIds: _children.map((c) => c.id).toSet(),
+      title: 'Rattacher un enfant',
     );
     if (selected == null || !mounted) return;