refactor(#93): extraire un widget UserList réutilisable

Centralise le pattern d'affichage des listes utilisateurs pour garantir une UI homogène entre gestionnaires, parents, assistantes maternelles et administrateurs.

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

frontend/lib/widgets/admin/admin_management_widget.dart

@@ -1,8 +1,8 @@
 import 'package:flutter/material.dart';
 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_list_state.dart';
 import 'package:p_tits_pas/widgets/admin/common/admin_user_card.dart';
+import 'package:p_tits_pas/widgets/admin/common/user_list.dart';
 
 class AdminManagementWidget extends StatefulWidget {
   final String searchQuery;
@@ -60,42 +60,32 @@ class _AdminManagementWidgetState extends State<AdminManagementWidget> {
       return name.contains(query) || email.contains(query);
     }).toList();
 
-    return Padding(
-      padding: const EdgeInsets.all(16),
-      child: Column(
-        crossAxisAlignment: CrossAxisAlignment.stretch,
-        children: [
-          AdminListState(
-            isLoading: _isLoading,
-            error: _error,
-            isEmpty: filteredAdmins.isEmpty,
-            emptyMessage: 'Aucun administrateur trouvé.',
-            list: ListView.builder(
-              itemCount: filteredAdmins.length,
-              itemBuilder: (context, index) {
-                final user = filteredAdmins[index];
-                return AdminUserCard(
-                  title: user.fullName,
-                  subtitleLines: [
-                    user.email,
-                    'Rôle : ${user.role}',
-                  ],
-                  avatarUrl: user.photoUrl,
-                  actions: [
-                    IconButton(
-                      icon: const Icon(Icons.edit),
-                      tooltip: 'Modifier',
-                      onPressed: () {
-                        // TODO: Modifier admin
-                      },
-                    ),
-                  ],
-                );
+    return UserList(
+      isLoading: _isLoading,
+      error: _error,
+      isEmpty: filteredAdmins.isEmpty,
+      emptyMessage: 'Aucun administrateur trouvé.',
+      itemCount: filteredAdmins.length,
+      itemBuilder: (context, index) {
+        final user = filteredAdmins[index];
+        return AdminUserCard(
+          title: user.fullName,
+          subtitleLines: [
+            user.email,
+            'Rôle : ${user.role}',
+          ],
+          avatarUrl: user.photoUrl,
+          actions: [
+            IconButton(
+              icon: const Icon(Icons.edit),
+              tooltip: 'Modifier',
+              onPressed: () {
+                // TODO: Modifier admin
               },
             ),
-          ),
-        ],
-      ),
+          ],
+        );
+      },
     );
   }
 }