feat(#135): mode édition dossier + ajout co-parent (squash develop).

Wizard edit famille/AM, POST co-parent, PATCH enfants avec photo.

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

frontend/lib/widgets/admin/dossiers_management_widget.dart

@@ -85,6 +85,7 @@ class _DossiersManagementWidgetState extends State<DossiersManagementWidget> {
       context: context,
       builder: (context) => ValidationDossierModal(
         numeroDossier: num,
+        openAsEdit: true,
         onClose: () => Navigator.of(context).pop(),
         onSuccess: () {
           Navigator.of(context).pop();