Refine Docker stack configuration

- Use mariadb:latest and wordpress:php8.4 floating tags
- Add private registry image name (hub.bundespruefstelle.ch/woocommerce)
- Add restart policies (always for prod, unless-stopped for dev)
- Move .env-dist to project root

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

docker/Dockerfile

@@ -48,7 +48,7 @@ RUN composer install --no-dev --optimize-autoloader --no-interaction
 ###############################################################################
 # Stage 4 — Final WordPress image
 ###############################################################################
-FROM wordpress:6.9.1-php8.4-apache AS wp_runtime
+FROM wordpress:php8.4 AS wp_runtime
 
 RUN curl -sSfL -o /usr/local/bin/wp \
       https://raw.githubusercontent.com/wp-cli/builds/gh-pages/phar/wp-cli.phar \