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

tests/Unit/Trait/HasLoggerTraitTest.php

@@ -1,4 +1,5 @@
 <?php
+
 declare(strict_types=1);
 
 namespace App\Tests\Unit\Trait;
@@ -7,10 +8,12 @@ use App\Trait\HasLoggerTrait;
 use PHPUnit\Framework\TestCase;
 use Psr\Log\LoggerInterface;
 
-final class HasLoggerTraitTest extends TestCase {
+final class HasLoggerTraitTest extends TestCase
+{
     use HasLoggerTrait;
 
-    public function testSetLogger(): void {
+    public function testSetLogger(): void
+    {
         $logger = $this->createStub(LoggerInterface::class);
         $this->setLogger($logger);
         self::assertSame($logger, $this->logger);