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>

configs/shared-vhost-template.tpl

@@ -0,0 +1,39 @@
+<Directory "/mnt/users/~~user~~/~~domain~~">
+    AllowOverride None
+    Require all granted
+</Directory>
+
+<Directory "/mnt/users/~~user~~/~~domain~~/public_html">
+    Options All MultiViews
+    AllowOverride All
+    Require all granted
+</Directory>
+
+<VirtualHost *:80>
+    ServerName "~~domain~~"
+    ~~alias_block~~
+    DocumentRoot "/mnt/users/~~user~~/~~domain~~/public_html"
+    RewriteEngine on
+    RewriteCond %{SERVER_NAME} =~~domain~~
+    RewriteRule ^ https://%{SERVER_NAME}%{REQUEST_URI} [END,NE,R=permanent]
+</VirtualHost>
+
+<IfModule mod_ssl.c>
+  <VirtualHost *:443>
+    ServerName "~~domain~~"
+    ~~alias_block~~
+    DocumentRoot "/mnt/users/~~user~~/~~domain~~/public_html"
+
+    SSLCertificateFile /etc/pki/tls/certs/localhost.crt
+    SSLCertificateKeyFile /etc/pki/tls/private/localhost.key
+
+    <FilesMatch \.php$>
+        SetHandler "proxy:fcgi://~~fpm_host~~:~~fpm_port~~"
+    </FilesMatch>
+
+    DirectoryIndex index.php index.html index.htm
+
+    ErrorLog "/var/log/httpd/~~domain~~-error.log"
+    CustomLog "/var/log/httpd/~~domain~~-access.log" combined
+  </VirtualHost>
+</IfModule>