chore: move php-cs-fixer config into tools

- relocate .php-cs-fixer.dist.php to tools/php-cs-fixer/.php-cs-fixer.dist.php

- update composer scripts, docs, quality gates, and style skill references

- keep finder scope stable via project-root resolution

- fix pre-existing unused imports reported by php-cs-fixer

tools/php-cs-fixer/.php-cs-fixer.dist.php

@@ -0,0 +1,21 @@
+<?php
+
+$projectRoot = dirname(__DIR__, 2);
+
+$finder = PhpCsFixer\Finder::create()
+    ->in([
+        $projectRoot . '/config',
+        $projectRoot . '/lib',
+        $projectRoot . '/pages',
+        $projectRoot . '/tests',
+    ])
+    ->name('*.php');
+
+return (new PhpCsFixer\Config())
+    ->setRiskyAllowed(false)
+    ->setRules([
+        '@PSR12' => true,
+        'ordered_imports' => ['sort_algorithm' => 'alpha'],
+        'no_unused_imports' => true,
+    ])
+    ->setFinder($finder);