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>

composer.json

@@ -30,7 +30,9 @@
         "behat/mink-browserkit-driver": "^2.0",
         "phpspec/phpspec": "^8.0",
         "symfony/browser-kit": "^7.4 || ^8.0",
-        "symfony/http-client": "^7.4 || ^8.0"
+        "symfony/http-client": "^7.4 || ^8.0",
+        "friendsofphp/php-cs-fixer": "^3.75",
+        "phpstan/phpstan": "^2.0"
     },
     "replace": {
         "behat/mink-extension": "self.version"
@@ -46,6 +48,9 @@
         }
     },
     "scripts": {
+        "cs": "vendor/bin/php-cs-fixer fix",
+        "cs-check": "vendor/bin/php-cs-fixer fix --dry-run",
+        "phpstan": "vendor/bin/phpstan analyse --memory-limit=512M",
         "test": [
             "vendor/bin/phpspec run -f pretty",
             "vendor/bin/behat --config behat.dist.php -fprogress --strict"