add option to indicate image copyright for summary preview

test_template/main.typ

@@ -172,6 +172,7 @@ thead {
       url: "http://test.example.com",
       title: "Card " + str(perm.at(i)),
       preview-image: summ.preview-image,
+      img-copyright: if calc.rem(i, 3) == 0 { [Histausse ] } else { none },
       author: "Me!",
       description: lorem(10 * calc.rem(i * 123,  10)),
       date: datetime(year: 2000, month: 12, day: perm.at(i)),