fix: add SPDX header

Signed-off-by: Vitor Mattos <1079143+vitormattos@users.noreply.github.com>

Author: vitormattos

src/views/Settings/SignatureEngine.vue

@@ -1,3 +1,7 @@
+<!--
+  - SPDX-FileCopyrightText: 2026 LibreCode coop and LibreCode contributors
+  - SPDX-License-Identifier: AGPL-3.0-or-later
+-->
 <template>
 	<NcSettingsSection
 		:name="t('libresign', 'Signature engine')"