Add shared httpd + PHP-FPM-only container architecture

Separate Apache and PHP-FPM into distinct container roles to reduce
per-customer memory overhead on shared servers. Adds three new images:
- Dockerfile.fpm: PHP-FPM only (no Apache), listens on TCP port 9000
- Dockerfile.shared-httpd: Apache only (no PHP), with SSL and proxy_fcgi
- Existing Dockerfile unchanged for standalone mode

Key changes:
- detect-memory.sh: CONTAINER_ROLE env var (combined/fpm_only/httpd_only)
  controls the memory budget split
- create-php-config.sh: FPM_LISTEN env var for TCP port vs Unix socket,
  added /fpm-ping and /fpm-status health endpoints
- New entrypoints for each container role
- tune-mpm.sh for hot-adjusting Apache MPM settings
- shared-vhost-template.tpl with proxy_fcgi and SSL on port 443
- CI/CD builds all three image types in parallel

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

Dockerfile.shared-httpd

@@ -0,0 +1,40 @@
+FROM almalinux/9-base
+
+# Install Apache and minimal dependencies (no PHP at all)
+RUN dnf install -y \
+      https://dl.fedoraproject.org/pub/epel/epel-release-latest-9.noarch.rpm && \
+    dnf update -y && \
+    dnf install -y httpd mod_ssl iproute cronie procps curl && \
+    dnf clean all && \
+    rm -rf /var/cache/dnf /usr/share/doc /usr/share/man /usr/share/locale/*
+
+# Copy scripts and set permissions
+COPY ./scripts/detect-memory.sh /scripts/detect-memory.sh
+COPY ./scripts/create-apache-mpm-config.sh /scripts/create-apache-mpm-config.sh
+COPY ./scripts/log-rotate.sh /scripts/log-rotate.sh
+COPY ./scripts/entrypoint-shared-httpd.sh /scripts/entrypoint-shared-httpd.sh
+COPY ./scripts/tune-mpm.sh /scripts/tune-mpm.sh
+RUN chmod +x /scripts/*
+
+# Generate self-signed SSL cert (same as main CAC image)
+RUN openssl req -newkey rsa:2048 -nodes \
+      -keyout /etc/pki/tls/private/localhost.key \
+      -x509 -days 3650 -subj "/CN=localhost" \
+      -out /etc/pki/tls/certs/localhost.crt
+
+# Copy Apache configs
+COPY ./configs/remote_ip.conf /etc/httpd/conf.d/
+COPY ./configs/default-index.conf /etc/httpd/conf.d/
+
+# Create vhosts directory (will be volume-mounted from host)
+RUN mkdir -p /etc/httpd/conf.d/vhosts
+
+# Set up cron job for log rotation
+RUN echo "15 */12 * * * root /scripts/log-rotate.sh" >> /etc/crontab
+
+EXPOSE 80 443
+
+HEALTHCHECK --interval=30s --timeout=5s --start-period=60s --retries=3 \
+  CMD curl -sfk https://localhost/ping || exit 1
+
+ENTRYPOINT [ "/scripts/entrypoint-shared-httpd.sh" ]