Refactor blocks architecture to modular approach

- Restore "1/2, 1/2" layout for flexible column combinations
- Simplify beforeafter block: remove toggle and text field, keep only image comparison
- Create new video block with URL support (YouTube/Vimeo/direct files)
- Create horizontal-gallery block for scrollable image galleries
- Add H4 heading level support
- All blocks now modular: combine with text blocks in 2-column layouts

Blocks available:
- Text, Heading (h2-h4), Image, Video
- Before/After comparison (no text)
- Horizontal gallery (with text below)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

site/plugins/video/snippets/blocks/video.php

@@ -0,0 +1,39 @@
+<?php
+/** @var \Kirby\Cms\Block $block */
+$url = $block->url()->value();
+$caption = $block->caption()->value();
+
+// Fonction pour détecter le type de vidéo
+function getVideoEmbedCode($url) {
+    // YouTube
+    if (preg_match('/youtube\.com\/watch\?v=([^&]+)/', $url, $matches) ||
+        preg_match('/youtu\.be\/([^?]+)/', $url, $matches)) {
+        $videoId = $matches[1];
+        return '<iframe src="https://www.youtube.com/embed/' . $videoId . '" frameborder="0" allowfullscreen></iframe>';
+    }
+
+    // Vimeo
+    if (preg_match('/vimeo\.com\/(\d+)/', $url, $matches)) {
+        $videoId = $matches[1];
+        return '<iframe src="https://player.vimeo.com/video/' . $videoId . '" frameborder="0" allowfullscreen></iframe>';
+    }
+
+    // Vidéo directe (mp4, webm, etc.)
+    if (preg_match('/\.(mp4|webm|ogg)$/i', $url)) {
+        return '<video controls><source src="' . $url . '" type="video/' . pathinfo($url, PATHINFO_EXTENSION) . '"></video>';
+    }
+
+    // Par défaut, iframe
+    return '<iframe src="' . $url . '" frameborder="0" allowfullscreen></iframe>';
+}
+?>
+
+<?php if ($url): ?>
+<div class="container-video">
+    <?= getVideoEmbedCode($url) ?>
+</div>
+
+<?php if ($caption): ?>
+<p class="caption"><?= $caption ?></p>
+<?php endif ?>
+<?php endif ?>