fix(control-panel): correct WordPress image tag template

The official WordPress php-fpm images tag PHP as `phpX.Y` (e.g.
wordpress:php8.3-fpm-alpine), not `X.Y`. The images.wordpress default rendered
`wordpress:8.3-fpm-alpine`, which does not exist ("manifest unknown"). Add the
`php` prefix so the wordpress profile pulls a real image.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

control-panel/config.example.yaml

@@ -14,7 +14,7 @@ registry: git.example.com/heleos
 images:
   nginx: "{registry}/nginx:latest"
   php_fpm: "{registry}/php-fpm:{php_version}"
-  wordpress: "wordpress:{php_version}-fpm-alpine"
+  wordpress: "wordpress:php{php_version}-fpm-alpine"
 
 # Shared MariaDB. Root password is read from this .env (or the
 # MARIADB_ROOT_PASSWORD environment variable).