CodeIgniter 3.1.11 -> 3.4.5 (pocketarc fork) en PHP 8.3-fixes

- system/ vervangen door CodeIgniter 3.4.5 (pocketarc/codeigniter, PHP 8.2-8.5 compatibel)
- config.php, mimes.php, user_agents.php en error-views bijgewerkt naar 3.4.5
- composer.json: php-constraint "^7.4 || ^8.0" zodat composer install op 8.3 werkt
- PHP 8-fatals opgelost: count()/array-functies op FALSE/null, rekenen met lege
  strings, delen door nul, property zetten op FALSE, curly-brace string offsets,
  ongedefinieerde constanten, foute curl_setopt in Phantom_model::create_img
- dynamic properties gedeclareerd in libraries, optionele parameters voor verplichte opgelost
- vergelijkingen waar '' == 0 in PHP 8 anders uitvalt gecast naar (int)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

system/libraries/Trackback.php

@@ -6,7 +6,7 @@
  *
  * This content is released under the MIT License (MIT)
  *
- * Copyright (c) 2014 - 2019, British Columbia Institute of Technology
+ * Copyright (c) 2019 - 2022, CodeIgniter Foundation
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -30,6 +30,7 @@
  * @author	EllisLab Dev Team
  * @copyright	Copyright (c) 2008 - 2014, EllisLab, Inc. (https://ellislab.com/)
  * @copyright	Copyright (c) 2014 - 2019, British Columbia Institute of Technology (https://bcit.ca/)
+ * @copyright	Copyright (c) 2019 - 2022, CodeIgniter Foundation (https://codeigniter.com/)
  * @license	https://opensource.org/licenses/MIT	MIT License
  * @link	https://codeigniter.com
  * @since	Version 1.0.0
@@ -46,7 +47,7 @@ defined('BASEPATH') OR exit('No direct script access allowed');
  * @subpackage	Libraries
  * @category	Trackbacks
  * @author		EllisLab Dev Team
- * @link		https://codeigniter.com/user_guide/libraries/trackback.html
+ * @link		https://codeigniter.com/userguide3/libraries/trackback.html
  */
 class CI_Trackback {