pops-restore: --list to show the available backups #111

Context

pops-backup writes one folder per backup under BACKUP_DIR (default /var/backups/pops, set in /etc/pops/backup.conf), named by UTC time, e.g. 20260929T023000Z. Each folder holds db.dump, files.tgz, SHA256SUMS and meta.json (created_at, version, db_name, pg_dump, …). Failed runs are kept as *.failed for a while.

To restore, an operator has to pass one of these folders to pops-restore. Today they have to ls the directory and open meta.json by hand to see which backup is which.

What to do

Add pops-restore --list:

• read BACKUP_DIR from the same config file pops-restore already sources (POPS_BACKUP_CONF, default /etc/pops/backup.conf), default /var/backups/pops;
• print one line per backup folder, newest first: folder name, created_at and version from meta.json, and the size (du -sh);
• mark *.failed folders, and folders without SHA256SUMS or meta.json, as not restorable;
• touch nothing: no database, no service, no files.

Acceptance criteria

• pops-restore --list works without root when BACKUP_DIR is readable, and changes nothing.
• --list together with a backup folder or with --yes/--check stops with a clear error.
• jq is not required: read meta.json with the tools the script already uses (sed/grep), or python3.
• The -h help text (the comment block at the top) and docs/backup.md describe the option.
• The Backup and restore job in .github/workflows/ci.yml calls Installer/server/pops-restore --list after the first backup and checks that the folder appears in the output.
• shellcheck --severity=warning Installer/server/pops-restore is clean (CI checks it).

Comments in the script are in Turkish; keep them in Turkish. Output messages may follow the existing [pops-restore] style.