DONE: fix mysql service cannot communicate

be/docker-compose.yml

@@ -3,9 +3,8 @@ services:
     image: mysql:8
     container_name: qms-mysql
     restart: unless-stopped
-    ports:
-      # Host port can be changed via MYSQL_HOST_PORT in .env (default 3306)
-      - "${MYSQL_HOST_PORT:-3306}:3306"
+    # Do not publish 3306 to the host — avoids clashes with host MySQL.
+    # Backend reaches it as hostname "mysql" on the internal Docker network.
     environment:
       MYSQL_ROOT_PASSWORD: ${MYSQL_ROOT_PASSWORD:-password}
       MYSQL_DATABASE: ${MYSQL_DATABASE:-qms}