Enforce roles on admin endpoints and return real status codes

- users, SMTP and batch-lock endpoints are owner/admin only
- engines answer 400/403/404/409/500 instead of 200 with an error body;
  database errors no longer leak to the client

app/accounting/api/engine/remove_department.php

@@ -6,7 +6,7 @@ require_once '../../../assets/utils/classes_ac/DepartmentManager.php';
 require_role($user_role, ['owner', 'admin']);
 
 $id = (int)($data['id'] ?? 0);
-if (!$id) { $answer['message'] = 'Missing id'; exit(json_encode($answer)); }
+if (!$id) { http_response_code(400); $answer['message'] = 'Missing id'; exit(json_encode($answer)); }
 
 $dept = new DepartmentManager($pdo2, $company_id);
 $dept->delete($id);