Fix: install gnupg before OpenResty apt key dearmoring

gpg is not present in python:3.12-slim-bookworm base image.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker/Dockerfile

@@ -58,6 +58,7 @@ RUN set -eux; \
     if [ "$WITH_POPPLER" = "1" ]; then apt-get install -y --no-install-recommends poppler-utils; fi; \
     if [ "$WITH_PSQL_CLIENT" = "1" ]; then apt-get install -y --no-install-recommends postgresql-client; fi; \
     if [ "$WITH_NGINX" = "1" ]; then \
+      apt-get install -y --no-install-recommends gnupg; \
       curl -fsSL https://openresty.org/package/pubkey.gpg | gpg --dearmor -o /usr/share/keyrings/openresty.gpg; \
       echo "deb [signed-by=/usr/share/keyrings/openresty.gpg] http://openresty.org/package/debian bookworm openresty" \
         > /etc/apt/sources.list.d/openresty.list; \