Feat: page Play — backgroundColor, playLink, play-icon + fix slug jouer

- Renommage dossier content 3_play → 3_jouer (slug /jouer)
- Champ backgroundColor (code-editor) dans game.yml + exposé en API
- playLinks simplifié en champ url simple → playLink dans l'API
- Variable CSS --background-color sur la section .play
- Bouton "Jouer" avec icône play-icon (SVG data URI dans buttons.css)
- Plugin sylvainjule/code-editor ajouté via composer

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

vendor/composer/autoload_psr4.php

@@ -16,7 +16,7 @@ return array(
     'PHPMailer\\PHPMailer\\' => array($vendorDir . '/phpmailer/phpmailer/src'),
     'League\\ColorExtractor\\' => array($vendorDir . '/league/color-extractor/src'),
     'Laminas\\Escaper\\' => array($vendorDir . '/laminas/laminas-escaper/src'),
-    'Kirby\\' => array($vendorDir . '/getkirby/composer-installer/src', $baseDir . '/kirby/src'),
+    'Kirby\\' => array($baseDir . '/kirby/src', $vendorDir . '/getkirby/composer-installer/src'),
     'Composer\\Semver\\' => array($vendorDir . '/composer/semver/src'),
     'Base32\\' => array($vendorDir . '/christian-riesen/base32/src'),
 );