fix : install docker-compose-plugin in prod Dockerfile

Deploy scripts use `docker compose` (Compose V2 plugin) which is not
included in docker.io package.

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

infra/prod/Dockerfile

@@ -40,7 +40,7 @@ FROM php:8.4-fpm AS production
 
 RUN apt-get update && apt-get install -y \
         libicu-dev libpq-dev libpng-dev libzip-dev libxml2-dev \
-        nginx supervisor docker.io \
+        nginx supervisor docker.io docker-compose-plugin \
     && docker-php-ext-install -j$(nproc) intl pdo_pgsql zip gd opcache \
     && rm -rf /var/lib/apt/lists/*