Add manual world backup script

Flushes world via rcon (save-off + save-all flush) before tarring
when the server is running; skips the flush and archives as-is when
the container is down. Outputs timestamped archives to backups/,
which is gitignored.

.gitignore

@@ -13,6 +13,7 @@ data/.rcon-cli.yaml
 # Backup snapshots
 data.*.bak/
 *.bak/
+backups/
 
 # Port-forward runtime state
 portforward.log