fix(ci): capture rpm --addsign output to file for error reporting

Direct stdout/stderr capture may miss gpg subprocess output. Write
to a temp file and cat it on failure.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

script/publish-repo.sh

@@ -9,8 +9,9 @@ REMOTE_DIR="/var/www/rpm/fedora/${FEDORA_VERSION}/x86_64"
 # sign each rpm with the imported gpg key
 for rpm in "${RPM_DIR}"/*.rpm; do
     echo "signing ${rpm}..."
-    if ! rpm --addsign "${rpm}" 2>&1; then
-        echo "failed to sign ${rpm}" >&2
+    if ! rpm --addsign "${rpm}" > /tmp/rpmsign.log 2>&1; then
+        echo "failed to sign ${rpm}:" >&2
+        cat /tmp/rpmsign.log >&2
         exit 1
     fi
 done