DONE: put hardcoded app_key for testing

be/docker/common/unified/Dockerfile

@@ -138,7 +138,11 @@ EXPOSE 80 9000
 # Start supervisor which manages both Nginx and PHP-FPM
 CMD ["supervisord", "-c", "/etc/supervisor/supervisord.conf"]
 
-# CI: install dev dependencies and run PHPUnit (build fails if tests fail)
+# CI: install dev dependencies and run PHPUnit (build with --target backend-test)
 FROM builder AS backend-test
+ENV APP_KEY=base64:2fl3rk3lI6+k9tJ0lZp2aXh6sL9mN4pQ7rT1vW5yZ8A=
 RUN composer install --no-interaction --prefer-dist --no-scripts \
     && ./vendor/bin/phpunit --no-coverage
+
+# Default production image target (use --target base for deploy builds)
+FROM base AS production