fix(auth): prevent system roles from being updated

- throw error in updateRole when role is system-protected
- hide edit button in roles table for system roles
- update README to reflect roles cannot be modified (not just renamed)

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

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