feat(#140): dashboard admin ch.6 — fiche parent, enfants, affiliation

Back: PATCH /parents/:id/fiche, attach/detach enfant, GET /enfants enrichi.
Front: modale parent éditable, onglet Enfants, fiche enfant, UserService.

Couvre doc 28 §6.1–6.2 ; tickets liés #115 #116 #130 #131 #137 #138.
Hors scope: fiche AM (#131), création admin (#129).

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

frontend/lib/models/parent_child_summary.dart

@@ -0,0 +1,31 @@
+/// Résumé enfant affiché dans la fiche parent (dashboard admin).
+class ParentChildSummary {
+  final String id;
+  final String? firstName;
+  final String? lastName;
+  final String status;
+
+  ParentChildSummary({
+    required this.id,
+    this.firstName,
+    this.lastName,
+    required this.status,
+  });
+
+  String get fullName {
+    final fn = (firstName ?? '').trim();
+    final ln = (lastName ?? '').trim();
+    if (fn.isEmpty && ln.isEmpty) return 'Enfant';
+    if (ln.isEmpty) return fn;
+    return '$fn $ln';
+  }
+
+  factory ParentChildSummary.fromJson(Map<String, dynamic> json) {
+    return ParentChildSummary(
+      id: (json['id'] ?? '').toString(),
+      firstName: json['first_name'] as String?,
+      lastName: json['last_name'] as String?,
+      status: (json['status'] ?? '').toString(),
+    );
+  }
+}