Add PHP CS Fixer and PHPStan max to CI; remove abandoned GoutteFactory

- Add friendsofphp/php-cs-fixer ^3.75 and phpstan/phpstan ^2.0 to
  require-dev; add .php-cs-fixer.dist.php (@Symfony ruleset with
  phpdoc_to_comment ignored_tags) and phpstan.neon (level max,
  treatPhpDocTypesAsCertain: false)
- Run CS Fixer and PHPStan in every CI matrix job alongside tests
- Add composer scripts: cs, cs-check, phpstan
- Add .php-cs-fixer.cache to .gitignore
- Fix all PHPStan max violations across src/: add return/param types,
  narrow mixed config values with is_string()/is_array() guards,
  use TaggedNodeInterface for scenario tag access in SessionsListener
- Remove GoutteFactory and its spec — the goutte driver and its
  underlying client library are abandoned

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

spec/Behat/MinkExtension/Context/Initializer/MinkAwareInitializerSpec.php

@@ -9,25 +9,25 @@ use PhpSpec\ObjectBehavior;
 
 class MinkAwareInitializerSpec extends ObjectBehavior
 {
-    function let(Mink $mink)
+    public function let(Mink $mink)
     {
-        $this->beConstructedWith($mink, array('base_url' => 'foo'));
+        $this->beConstructedWith($mink, ['base_url' => 'foo']);
     }
 
-    function it_is_a_context_initializer()
+    public function it_is_a_context_initializer()
     {
         $this->shouldHaveType('Behat\Behat\Context\Initializer\ContextInitializer');
     }
 
-    function it_does_nothing_for_basic_contexts(Context $context)
+    public function it_does_nothing_for_basic_contexts(Context $context)
     {
         $this->initializeContext($context);
     }
 
-    function it_injects_mink_and_parameters_in_mink_aware_contexts(MinkAwareContext $context, $mink)
+    public function it_injects_mink_and_parameters_in_mink_aware_contexts(MinkAwareContext $context, $mink)
     {
         $context->setMink($mink)->shouldBeCalled();
-        $context->setMinkParameters(array('base_url' => 'foo'))->shouldBeCalled();
+        $context->setMinkParameters(['base_url' => 'foo'])->shouldBeCalled();
         $this->initializeContext($context);
     }
 }