Backup server: skip self-pruning repos in remote-prune

backup_server_remote_skip lists apps whose client prunes the repository itself; remote-prune without arguments leaves them alone (an explicit app list still works).

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

templates/opt/backup/inst/cloud-server-backup.j2

@@ -7,6 +7,8 @@ LOCALREPOLOCATION="{{ backup_location }}/{{ backup_app }}";
 APPLIST="{{ server_clients | json_query('*.app') | join(' ') }}";
 # repos that are only pruned remotely, not mirrored locally
 LOCALAPPLIST="{{ server_clients | json_query('*.app') | difference(backup_server_local_skip) | join(' ') }}";
+# repos pruned by their own client (e.g. a NAS borg plugin), skipped by remote-prune without arguments
+REMOTEPRUNEAPPLIST="{{ server_clients | json_query('*.app') | difference(backup_server_remote_skip) | join(' ') }}";
 MIRRORFOLDER="{{ backup_server_mirror | default(backup_remotes_folder) }}";
 
 declare -A BORG_CLIENT_MAP
@@ -246,7 +248,11 @@ local_delete () {
             ;;
 
         "remote-prune")
-            USERLIST=$(validate_apps_or_default "$2");
+            if [[ -z "$2" ]]; then
+                USERLIST=$REMOTEPRUNEAPPLIST;
+            else
+                USERLIST=$(validate_apps_or_default "$2");
+            fi
             remote_prune "$USERLIST";
             ;;