If you set it's download folder in the .env to the same as the ingestion folder for Calibre, it'll just show up. Set -no-browser-downloads and it'll just drop that into the folder and won't prompt you to save it manually.

***
version: "2.1"
services:
  calibre:
    image: lscr.io/linuxserver/calibre:latest
    container_name: calibre
    environment:
      - PUID=0
      - PGID=0
      - TZ=America/Denver
    security_opt:
      - seccomp=unconfined
    volumes:
      - ./data:/config
    ports:
      - 7080:8080
      - 7081:8081
      - 7181:8181
    restart: unless-stopped
    labels:
      - com.centurylinklabs.watchtower.enable=true

  openbooks:
    ports:
      - 7082:80
    volumes:
      - './data/:/books'
    restart: unless-stopped
    container_name: calibre-openbooks
#    command: --persist
    command: --name asdasuu6ghgf --persist --no-browser-downloads
    environment:
      - BASE_PATH=/
    image: evanbuss/openbooks:latest
    labels:
      - com.centurylinklabs.watchtower.enable=true

You'll have to manually set the ingest folder in Calibre in the the setting to this folder that shows in the calibre container as "config" (or maybe just the root folder, can't recall)