// Path to app/Config/Paths.php
$pathsConfig = FCPATH . './Config/Paths.php'; // assuming app folder is backend/app
require realpath($pathsConfig) ?: $pathsConfig;

$paths = new Config\Paths();

// Location of the framework bootstrap file.
$bootstrap = rtrim($paths->systemDirectory, '\\/ ') . DIRECTORY_SEPARATOR . 'bootstrap.php';
$app       = require realpath($bootstrap) ?: $bootstrap;

$app->run();