The gitnexus droplet is ~8.7GB usable, not the 60GB the disk-cleanup
comment assumed. With /usr (~2.8GB), the in-use docker images (~2.1GB),
and the growing /opt/gitnexus/indexes (~1.2GB), deploys were aborting at
the `AVAIL_MB < 2048` guard ("Disk critically low").
Two fixes:
- Reclaim the previous gitnexus image after force-recreate. The pre-pull
`docker system prune -af` cannot remove it while the old container is
still running, so a stale ~700MB generation accumulated every deploy.
A post-recreate `docker image prune -f` makes the box self-cleaning.
- Lower the abort threshold 2048 -> 1536MB. The image is ~700MB and
shares most layers with the running one, so an incremental pull needs
well under 1GB; the old guard was sized for the 60GB assumption.
Also corrects the stale 60GB comment to reflect the actual disk.