Install PHP Xdebug debugger (#1399)

While working in a non-trivial feature, debugging support was needed.
Since Xdebug is the official PHP debugger, is available in Arch's
official repositories, and is trivial to configure, it makes sense to
include it in the PHP development environment.

This addition improves the overall development experience for PHP
developers by enabling easier inspection and troubleshooting.

With this PR, the debugger now shows up an enabled extension:

```
$ php -v

PHP 8.4.12 (cli) (built: Aug 27 2025 06:23:40) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.4.12, Copyright (c) Zend Technologies
    with Xdebug v3.4.4, Copyright (c) 2002-2025, by Derick Rethans
```

bin/omarchy-install-dev-env

@@ -6,7 +6,7 @@ if [[ -z "$1" ]]; then
 fi
 
 install_php() {
-  sudo pacman -S php composer php-sqlite --noconfirm
+  sudo pacman -S php composer php-sqlite xdebug --noconfirm
 
   # Install Path for Composer
   if [[ ":$PATH:" != *":$HOME/.config/composer/vendor/bin:"* ]]; then
@@ -28,6 +28,12 @@ install_php() {
     "pdo_mysql"
   )
 
+  # Enable Xdebug
+  sudo sed -i \
+    -e 's/^;zend_extension=xdebug.so/zend_extension=xdebug.so/' \
+    -e 's/^;xdebug.mode=debug/xdebug.mode=debug/' \
+    /etc/php/conf.d/xdebug.ini
+
   for ext in "${extensions_to_enable[@]}"; do
     sudo sed -i "s/^;extension=${ext}/extension=${ext}/" "$php_ini_path"
   done