chore(docker): restrict Postgres port exposure to localhost in production configuration

docker-compose.prod.yml

@@ -9,6 +9,8 @@ services:
       POSTGRES_DB: ${POSTGRES_DB:-app}
     networks:
       - nw_memegoat
+    ports:
+      - "127.0.0.1:5432:5432"    # not exposed to WAN, LAN only for administration checkup
     volumes:
       - postgres_data:/var/lib/postgresql/data
     healthcheck: