Add --pinentry-mode loopback to GPG plugin for non-interactive signing

CI was failing because GPG tried to open an interactive pinentry prompt.
This flag allows GPG to accept the passphrase via stdin in headless
environments like GitHub Actions.

https://claude.ai/code/session_01ToqqHtNtg7kdm8TmAMZYe8

Author: claude

pom.xml

@@ -199,6 +199,10 @@
         <version>3.2.8</version>
         <configuration>
           <keyname>FB32919AB5830162299F4125C49AB890BA00B57D</keyname>
+          <gpgArguments>
+            <arg>--pinentry-mode</arg>
+            <arg>loopback</arg>
+          </gpgArguments>
         </configuration>
         <executions>
           <execution>