enh(shopware): improve healthchecks and proxy configuration

Removed obsolete EXPOSE/healthcheck from Dockerfile and added robust service-specific healthchecks:

- web: HTTP robots.txt check

- worker/scheduler: php -v runtime check

- opensearch: cluster health API check

Added TRUSTED_PROXIES=* for proxy-aware headers and centralized OPENSEARCH_PORT in vars.

Context: discussed implementation details in ChatGPT conversation on 2025-11-06 — https://chatgpt.com/share/690c9fb3-79f4-800f-bbdf-ea370c8f142c

roles/web-app-shopware/templates/Dockerfile.j2

@@ -85,8 +85,3 @@ RUN set -eux; \
 
 # Drop back to the app user
 USER www-data
-
-# Expose internal port & add a lightweight healthcheck
-EXPOSE 8000
-HEALTHCHECK --interval=30s --timeout=5s --retries=5 --start-period=20s \
-  CMD php -r '$s=@fsockopen("127.0.0.1", 8000, $e, $t, 3); if(!$s) exit(1); fclose($s);'