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/lib/DB.php

@@ -117,5 +117,9 @@ class DB {
         return $this->pdo->lastInsertId();
     }
 
+    public function beginTransaction(): void  { $this->pdo->beginTransaction(); }
+    public function commit(): void            { $this->pdo->commit(); }
+    public function rollback(): void          { if ($this->pdo->inTransaction()) $this->pdo->rollBack(); }
+
     public function pdo(): PDO { return $this->pdo; }
 }