fix: change backend host port 8080→8081 (conflict)

docker-compose.yml

@@ -2,7 +2,7 @@ services:
   backend:
     build: ./backend
     ports:
-      - "8080:8080"
+      - "8081:8080"
     environment:
       SPRING_DATASOURCE_URL: jdbc:postgresql://192.168.31.2:5432/sr_service_db
       SPRING_DATASOURCE_USERNAME: ${POSTGRES_USER:-sr_admin}