feat: Usa field_user_name como nome de exibição do usuário

Implementa hook_user_format_name_alter() para substituir o username pelo
valor de field_user_name em todo o site. Na view /admin/people o username
original é mantido alterando o formatter do campo name de user_name para
string, exibindo o valor bruto sem passar por getDisplayName().

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

config/optional/views.view.user_admin_people.yml

@@ -123,7 +123,7 @@ display:
           empty_zero: false
           hide_alter_empty: true
           click_sort_column: value
-          type: user_name
+          type: string
           settings:
             link_to_entity: true
           group_column: value

site_users.module

@@ -331,6 +331,18 @@ function site_users_user_presave(UserInterface $user) {
   }
 }
 
+/**
+ * Implements hook_user_format_name_alter().
+ */
+function site_users_user_format_name_alter(&$name, $account) {
+  if (!($account instanceof UserInterface)) {
+    return;
+  }
+  if ($account->hasField('field_user_name') && !$account->get('field_user_name')->isEmpty()) {
+    $name = $account->get('field_user_name')->value;
+  }
+}
+
 /**
  * Implements hook_site_tools_share_links().
  */