2. Обновим /admin/index.php

Теперь будем использовать метод render:

<?php
require_once '../engine/init.php';

// Проверка роли
if (!$user_id || $db->query("SELECT role FROM users WHERE id = $user_id")->fetch_assoc()['role'] !== 'admin') {
    header('Location: /login.php');
    exit;
}

$template->assign('title', 'Админ-панель - MasterOK CMS');
$template->render(ROOT_DIR . '/admin/templates/admin_main.tpl');

3. Обновим /admin/categories.php

<?php
require_once '../engine/init.php';

if (!$user_id || $db->query("SELECT role FROM users WHERE id = $user_id")->fetch_assoc()['role'] !== 'admin') {
    header('Location: /login.php');
    exit;
}

if ($_SERVER['REQUEST_METHOD'] == 'POST') {
    if (isset($_POST['add'])) {
        $name = $_POST['name'];
        $db->query("INSERT INTO categories (name) VALUES ('$name')");
    } elseif (isset($_POST['edit'])) {
        $id = $_POST['id'];
        $name = $_POST['name'];
        $db->query("UPDATE categories SET name = '$name' WHERE id = $id");
    } elseif (isset($_POST['delete'])) {
        $id = $_POST['id'];
        $db->query("DELETE FROM categories WHERE id = $id");
    }
}

$categories = $db->query("SELECT * FROM categories");
$list = '';
while ($cat = $categories->fetch_assoc()) {
    $list .= "<tr>
        <td>{$cat['id']}</td>
        <td>{$cat['name']}</td>
        <td>
            <form method='post' style='display:inline;'>
                <input type='hidden' name='id' value='{$cat['id']}'>
                <input type='text' name='name' value='{$cat['name']}' required>
                <button type='submit' name='edit' class='button small'>Сохранить</button>
            </form>
            <form method='post' style='display:inline;'>
                <input type='hidden' name='id' value='{$cat['id']}'>
                <button type='submit' name='delete' class='button small delete'>Удалить</button>
            </form>
        </td>
    </tr>";
}

$template->assign('title', 'Управление категориями');
$template->assign('categories', $list);
$template->render(ROOT_DIR . '/admin/templates/admin_categories.tpl');

4. Обновим /admin/users.php

<?php
require_once '../engine/init.php';

if (!$user_id || $db->query("SELECT role FROM users WHERE id = $user_id")->fetch_assoc()['role'] !== 'admin') {
    header('Location: /login.php');
    exit;
}

if ($_SERVER['REQUEST_METHOD'] == 'POST') {
    if (isset($_POST['edit'])) {
        $id = $_POST['id'];
        $role = $_POST['role'];
        $db->query("UPDATE users SET role = '$role' WHERE id = $id");
    } elseif (isset($_POST['delete'])) {
        $id = $_POST['id'];
        $db->query("DELETE FROM users WHERE id = $id");
    }
}

$users = $db->query("SELECT * FROM users");
$list = '';
while ($user = $users->fetch_assoc()) {
    $list .= "<tr>
        <td>{$user['id']}</td>
        <td>{$user['username']}</td>
        <td>{$user['first_name']} {$user['last_name']}</td>
        <td>{$user['phone']}</td>
        <td>
            <form method='post' style='display:inline;'>
                <input type='hidden' name='id' value='{$user['id']}'>
                <select name='role'>
                    <option value='user' " . ($user['role'] == 'user' ? 'selected' : '') . ">Заказчик</option>
                    <option value='freelancer' " . ($user['role'] == 'freelancer' ? 'selected' : '') . ">Фрилансер</option>
                    <option value='admin' " . ($user['role'] == 'admin' ? 'selected' : '') . ">Админ</option>
                </select>
                <button type='submit' name='edit' class='button small'>Сохранить</button>
            </form>
            <form method='post' style='display:inline;'>
                <input type='hidden' name='id' value='{$user['id']}'>
                <button type='submit' name='delete' class='button small delete'>Удалить</button>
            </form>
        </td>
    </tr>";
}

$template->assign('title', 'Управление пользователями');
$template->assign('users', $list);
$template->render(ROOT_DIR . '/admin/templates/admin_users.tpl');

5. Обновим /admin/orders.php

<?php
require_once '../engine/init.php';

if (!$user_id || $db->query("SELECT role FROM users WHERE id = $user_id")->fetch_assoc()['role'] !== 'admin') {
    header('Location: /login.php');
    exit;
}

if ($_SERVER['REQUEST_METHOD'] == 'POST' && isset($_POST['delete'])) {
    $id = $_POST['id'];
    $db->query("DELETE FROM orders WHERE id = $id");
}

$orders = $db->query("SELECT o.*, u.username FROM orders o LEFT JOIN users u ON o.user_id = u.id");
$list = '';
while ($order = $orders->fetch_assoc()) {
    $list .= "<tr>
        <td>{$order['id']}</td>
        <td>{$order['title']}</td>
        <td>{$order['username']}</td>
        <td>{$order['created_at']}</td>
        <td>
            <a href='/order.php?id={$order['id']}' class='button small'>Просмотр</a>
            <form method='post' style='display:inline;'>
                <input type='hidden' name='id' value='{$order['id']}'>
                <button type='submit' name='delete' class='button small delete'>Удалить</button>
            </form>
        </td>
    </tr>";
}

$template->assign('title', 'Управление заказами');
$template->assign('orders', $list);
$template->render(ROOT_DIR . '/admin/templates/admin_orders.tpl');