Backup server: incremental mirror, client subset, configurable compression

- local_backup rsynced every repository into an empty folder each night (full transfer); keep a persistent mirror (backup_server_mirror) and rsync --delete into it
- backup_server_clients: clients handled by the server (app names must be unique, e.g. two 'webserver' apps collided)
- backup_server_local_skip: apps that are pruned remotely but not mirrored
- backup_server_compression: borg repos are encrypted already, allow 'none'

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

defaults/main.yml

@@ -23,6 +23,12 @@ backup_cron_owner: "{{ backup_owner }}"
 backup_server_remote_prune_time: 6
 backup_server_remote_backup_time: 8
 backup_server_local_prune_time: 10
+#server: clients to prune/mirror (defaults to backup_clients), apps not mirrored locally, local compression
+backup_server_clients: "{{ backup_clients }}"
+backup_server_local_skip: []
+backup_server_compression: lzma
+#local mirror of the remote repositories (defaults to <backup_root>/storage/remote-backups)
+#backup_server_mirror: /mnt/nas/backup/mirror
 
 
 backup_script: