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/components/RoleEditModal.client.js

@@ -125,7 +125,6 @@ const RoleEditModal = ({ roleId, isOpen, onClose, onSaved }) => {
                             label="Nom du rôle"
                             value={name}
                             onChange={setName}
-                            disabled={isSystem}
                             placeholder="Éditeur, Modérateur..."
                             required
                         />
@@ -162,6 +161,7 @@ const RoleEditModal = ({ roleId, isOpen, onClose, onSaved }) => {
                                             onChange={() => togglePerm(perm.key)}
                                             label={perm.name}
                                             description={perm.description}
+                                            disabled={isSystem}
                                         />
                                     ))}
                                 </div>

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"