Add Signed PDF signing package (#960)

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

pkgbuilds/signed/signed.install

@@ -0,0 +1,12 @@
+post_install() {
+  command -v update-desktop-database >/dev/null 2>&1 && update-desktop-database -q
+  command -v gtk-update-icon-cache >/dev/null 2>&1 && gtk-update-icon-cache -q -t -f usr/share/icons/hicolor
+}
+
+post_upgrade() {
+  post_install
+}
+
+post_remove() {
+  post_install
+}