feat: squelette de l'extension Read More (config, i18n)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

i18n/en/ext.php

@@ -0,0 +1,11 @@
+<?php
+
+return [
+	'read_more' => [
+		'button' => 'Read more',
+		'height' => [
+			'label' => 'Collapsed height (px)',
+			'help' => 'Visible height of an article before the “Read more” button (100–2000).',
+		],
+	],
+];