Backups push automatically; the token is only for restore

Matches the master's tokenless-push change: pushBackup no longer waits
for master_backup_token — every instance with a uuid backs up on its
own, and the 5-minute tick force-pushes so a poisoned master copy
self-heals. The token now only gates pulling a backup back (restore),
so setup-linux.sh asks for it only when restoring and the Settings
help text says so.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/settings/page.tsx

@@ -347,8 +347,8 @@ export default function SettingsPage() {
                         <div>
                             <p className="text-sm font-medium text-slate-800">Backup token</p>
                             <p className="text-xs text-slate-400 mt-0.5">
-                                Enables encrypted settings + credentials backups to the master
-                                (its INSTANCE_BACKUP_TOKEN). Blank = backups off.
+                                Backups push automatically — this token (the master&apos;s
+                                INSTANCE_BACKUP_TOKEN) is only needed to restore one.
                             </p>
                             <p className="text-xs text-slate-400 mt-0.5">
                                 {backupStatus.at