Strip remaining FILE INFORMATION headers from all non-XML/README files

Removes DEFGROUP, INGROUP, PATH, VERSION, BRIEF metadata from:
- Root PHP files (index.php, custom.php, error.php, offline.php, component.php)
- Language INI files (en-GB, en-US)
- All index.html security stubs
- brand-showcase.html, theme-test.html

Copyright/SPDX block preserved in all files.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/custom.php

@@ -1,19 +1,9 @@
 <?php
-/* Copyright (C) 2026 Moko Consulting <hello@mokoconsulting.tech>
+/* Copyright (C) 2025 Moko Consulting <hello@mokoconsulting.tech>
 
  This file is part of a Moko Consulting project.
 
  SPDX-License-Identifier: GPL-3.0-or-later
-
-
-
- # FILE INFORMATION
- DEFGROUP: Joomla.Template.Site
- INGROUP: MokoCassiopeia
- REPO: https://github.com/mokoconsulting-tech/MokoCassiopeia
- PATH: ./templates/mokocassiopeia/custom.php
- VERSION: 03.09.02
- BRIEF: MokoCassiopeia with user-defined overrides
  */
 
 	function console_log($output, $with_script_tags = true) {