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>

site/plugins/code-editor/composer.json

@@ -0,0 +1,20 @@
+{
+	"name": "sylvainjule/code-editor",
+	"description": "Code editor field for Kirby 3, 4 and 5",
+	"type": "kirby-plugin",
+	"license": "MIT",
+	"version": "1.1.0",
+	"authors": [
+		{
+			"name": "Sylvain Julé",
+			"email": "contact@sylvain-jule.fr"
+		}
+	],
+	"require": {
+		"getkirby/composer-installer": "^1.2"
+	},
+	"extra": {
+		"installer-name": "code-editor"
+	},
+	"minimum-stability": "beta"
+}