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/horizontal-gallery/src/components/HorizontalGalleryBlock.vue

@@ -0,0 +1,142 @@
+<template>
+  <div @click="$emit('open')" class="hgallery-preview">
+    <div class="hgallery-preview__container">
+      <!-- Zone galerie horizontale -->
+      <div class="hgallery-preview__gallery">
+        <div v-if="images.length > 0" class="hgallery-preview__scroll">
+          <div
+            v-for="(image, index) in images"
+            :key="index"
+            class="hgallery-preview__slide"
+          >
+            <img :src="image.url" :alt="image.caption || 'Image'" />
+            <p v-if="image.caption" class="hgallery-preview__caption">
+              {{ image.caption }}
+            </p>
+          </div>
+        </div>
+        <div v-else class="hgallery-preview__empty">
+          Aucune image sélectionnée
+        </div>
+      </div>
+
+      <!-- Zone texte -->
+      <div v-if="content.text" class="hgallery-preview__text">
+        <div v-html="content.text"></div>
+      </div>
+    </div>
+  </div>
+</template>
+
+<script setup>
+import { computed } from "vue";
+
+const props = defineProps({
+  content: Object
+});
+
+const images = computed(() => {
+  if (!props.content?.images || !props.content.images.length) {
+    return [];
+  }
+
+  return props.content.images.map(file => ({
+    url: file.url,
+    caption: file.text || file.caption || null
+  }));
+});
+</script>
+
+<style scoped>
+.hgallery-preview {
+  cursor: pointer;
+  border-radius: var(--rounded);
+  overflow: hidden;
+  background: var(--color-background);
+  border: 1px solid var(--color-gray-300);
+}
+
+.hgallery-preview__container {
+  display: flex;
+  flex-direction: column;
+  gap: 1rem;
+  padding: 1rem;
+}
+
+/* Galerie horizontale scrollable */
+.hgallery-preview__gallery {
+  width: 100%;
+}
+
+.hgallery-preview__scroll {
+  display: flex;
+  gap: 1rem;
+  overflow-x: auto;
+  padding-bottom: 0.5rem;
+  scroll-behavior: smooth;
+}
+
+.hgallery-preview__scroll::-webkit-scrollbar {
+  height: 6px;
+}
+
+.hgallery-preview__scroll::-webkit-scrollbar-track {
+  background: var(--color-gray-200);
+  border-radius: 3px;
+}
+
+.hgallery-preview__scroll::-webkit-scrollbar-thumb {
+  background: var(--color-gray-400);
+  border-radius: 3px;
+}
+
+.hgallery-preview__scroll::-webkit-scrollbar-thumb:hover {
+  background: var(--color-gray-500);
+}
+
+.hgallery-preview__slide {
+  flex-shrink: 0;
+  width: 250px;
+  display: flex;
+  flex-direction: column;
+  gap: 0.5rem;
+}
+
+.hgallery-preview__slide img {
+  width: 100%;
+  height: 180px;
+  object-fit: cover;
+  border-radius: var(--rounded-sm);
+  background: var(--color-gray-200);
+}
+
+.hgallery-preview__caption {
+  font-size: var(--text-xs);
+  color: var(--color-gray-600);
+  font-style: italic;
+  margin: 0;
+  line-height: 1.4;
+}
+
+.hgallery-preview__empty {
+  padding: 3rem 1rem;
+  text-align: center;
+  color: var(--color-gray-500);
+  font-size: var(--text-sm);
+  background: var(--color-gray-100);
+  border-radius: var(--rounded-sm);
+}
+
+/* Zone texte */
+.hgallery-preview__text {
+  font-size: var(--text-sm);
+  color: var(--color-gray-700);
+  line-height: 1.5;
+  padding-top: 0.5rem;
+  border-top: 1px solid var(--color-gray-200);
+}
+
+.hgallery-preview:hover {
+  border-color: var(--color-gray-400);
+}
+</style>