chore: add php-cs-fixer with PSR-12 config and CI check

- Add friendsofphp/php-cs-fixer to require-dev
- Create .php-cs-fixer.dist.php configured for @PSR12 ruleset
- Add php-cs-fixer dry-run step to CI pipeline
- Auto-fix existing PSR-12 violations
- Document code style tooling in readme.md

src/Trait/StringTrait.php

@@ -1,13 +1,16 @@
 <?php
+
 declare(strict_types=1);
 
 namespace App\Trait;
 
-trait StringTrait {
+trait StringTrait
+{
     /* cache keys can safely use alphanumeric, "_", and ".", remove the rest */
     private const string KEY_REGEX = '/[^A-Za-z0-9_.]+/';
 
-    public function makeCacheKey(string $name): string {
+    public function makeCacheKey(string $name): string
+    {
         return mb_substr(preg_replace(static::KEY_REGEX, '_', $name), 0, 128);
     }
 }