feat(users): allow system roles to be renamed but not have permissions changed

- update `updateRole` to allow name changes for system roles while blocking permission updates
- remove edit button restriction for system roles in roles page
- disable name field only was replaced by disabling permissions checkboxes for system roles in edit modal
- update README to reflect new system role update policy

src/features/admin/pages/RolesPage.client.js

@@ -81,15 +81,13 @@ const RolesPageClient = ({ canManage }) => {
             align: 'right',
             render: (role) => (
                 <div className="flex items-center justify-end gap-2">
-                    {!role.is_system && (
-                        <Button
-                            variant="secondary"
-                            onClick={() => openEdit(role.id)}
-                            icon={PencilEdit01Icon}
-                        >
-                            Modifier
-                        </Button>
-                    )}
+                    <Button
+                        variant="secondary"
+                        onClick={() => openEdit(role.id)}
+                        icon={PencilEdit01Icon}
+                    >
+                        Modifier
+                    </Button>
                     {!role.is_system && (
                         <Button
                             variant="danger"