fix(#138): enrichir les noms des responsables sur GET enfant.

GET /enfants/:id ne joint pas parent.user ; on complète les noms via
GET parent pour l'affichage des liens (ex. ouverture depuis la fiche AM).

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

frontend/lib/models/enfant_admin_model.dart

@@ -37,6 +37,34 @@ class EnfantAdminModel {
     return '$fn $ln';
   }
 
+  EnfantAdminModel copyWith({
+    String? id,
+    String? firstName,
+    String? lastName,
+    String? gender,
+    String? birthDate,
+    String? dueDate,
+    String? status,
+    String? photoUrl,
+    bool? consentPhoto,
+    bool? isMultiple,
+    List<EnfantParentLink>? parentLinks,
+  }) {
+    return EnfantAdminModel(
+      id: id ?? this.id,
+      firstName: firstName ?? this.firstName,
+      lastName: lastName ?? this.lastName,
+      gender: gender ?? this.gender,
+      birthDate: birthDate ?? this.birthDate,
+      dueDate: dueDate ?? this.dueDate,
+      status: status ?? this.status,
+      photoUrl: photoUrl ?? this.photoUrl,
+      consentPhoto: consentPhoto ?? this.consentPhoto,
+      isMultiple: isMultiple ?? this.isMultiple,
+      parentLinks: parentLinks ?? this.parentLinks,
+    );
+  }
+
   factory EnfantAdminModel.fromJson(Map<String, dynamic> json) {
     final linksRaw = json['parentLinks'] as List?;
     final links = <EnfantParentLink>[];
@@ -106,6 +134,13 @@ class EnfantParentLink {
 
   EnfantParentLink({required this.parentId, this.parentName});
 
+  EnfantParentLink copyWith({String? parentId, String? parentName}) {
+    return EnfantParentLink(
+      parentId: parentId ?? this.parentId,
+      parentName: parentName ?? this.parentName,
+    );
+  }
+
   factory EnfantParentLink.fromJson(Map<String, dynamic> json) {
     final parentId =
         (json['parentId'] ?? json['id_parent'] ?? '').toString();
@@ -116,6 +151,12 @@ class EnfantParentLink {
       if (user is Map<String, dynamic>) {
         final u = AppUser.fromJson(user);
         name = u.fullName.isNotEmpty ? u.fullName : u.email;
+      } else {
+        // Parfois le parent est aplati (prenom/nom) sans nested user.
+        final prenom = (parent['prenom'] ?? parent['first_name'] ?? '').toString().trim();
+        final nom = (parent['nom'] ?? parent['last_name'] ?? '').toString().trim();
+        final flat = '$prenom $nom'.trim();
+        if (flat.isNotEmpty) name = flat;
       }
     }
     return EnfantParentLink(