Run panel on dedicated novacpx-web Nginx service; fix auth/transaction methods

- deploy/nginx-panel.conf: standalone Nginx config for ports 8880-8883
- deploy/novacpx-web.service: systemd unit, survives apache2/nginx stop
- server_setup.php: fix Auth::requireRole() -> require('admin')
- DB.php: add beginTransaction()/commit()/rollback() methods

panel/api/endpoints/server_setup.php

@@ -4,7 +4,7 @@
  */
 $db   = DB::getInstance();
 $body = json_decode(file_get_contents('php://input'), true) ?? [];
-Auth::getInstance()->requireRole(['admin']);
+Auth::getInstance()->require('admin');
 
 function getSetting(string $key, $db): ?string {
     return $db->fetchOne("SELECT value FROM settings WHERE `key` = ?", [$key])['value'] ?? null;