Add before/after comparison block plugin

- Create custom block plugin with Vue 3 + Composition API
- Use kirbyup for building Vue SFC components
- Block allows selecting two images with slider comparison UI
- Preview shows images overlapped at 50% in the panel
- Add beforeafter block to report blueprint
- Update report template to use authors field
- Change text block heading level from 4 to 3

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

site/plugins/beforeafter/src/components/BeforeAfterBlock.vue

@@ -0,0 +1,118 @@
+<template>
+  <div @click="$emit('open')" class="beforeafter-preview">
+    <div v-if="hasImages" class="beforeafter-preview__images">
+      <img
+        v-if="imageBeforeUrl"
+        :src="imageBeforeUrl"
+        class="beforeafter-preview__image beforeafter-preview__image--before"
+        alt="Avant"
+      />
+      <img
+        v-if="imageAfterUrl"
+        :src="imageAfterUrl"
+        class="beforeafter-preview__image beforeafter-preview__image--after"
+        alt="Après"
+      />
+      <div v-if="imageBeforeUrl && imageAfterUrl" class="beforeafter-preview__divider"></div>
+    </div>
+
+    <p v-if="content.caption" class="beforeafter-preview__caption">
+      {{ content.caption }}
+    </p>
+
+    <div v-if="!hasImages" class="beforeafter-preview__empty">
+      Cliquer pour ajouter des images
+    </div>
+  </div>
+</template>
+
+<script setup>
+import { computed } from "vue";
+
+const props = defineProps({
+  content: Object,
+  endpoints: Object
+});
+
+const imageBeforeUrl = computed(() => {
+  // Attention: la clé est en minuscules dans Kirby
+  if (!props.content?.imagebefore || !props.content.imagebefore.length) {
+    return null;
+  }
+  const file = props.content.imagebefore[0];
+  return file?.url || null;
+});
+
+const imageAfterUrl = computed(() => {
+  // Attention: la clé est en minuscules dans Kirby
+  if (!props.content?.imageafter || !props.content.imageafter.length) {
+    return null;
+  }
+  const file = props.content.imageafter[0];
+  return file?.url || null;
+});
+
+const hasImages = computed(() => {
+  return imageBeforeUrl.value || imageAfterUrl.value;
+});
+</script>
+
+<style scoped>
+.beforeafter-preview {
+  cursor: pointer;
+  border-radius: var(--rounded);
+  overflow: hidden;
+  background: var(--color-background);
+}
+
+.beforeafter-preview__images {
+  position: relative;
+  width: 100%;
+  height: 200px;
+  background: var(--color-gray-200);
+}
+
+.beforeafter-preview__image {
+  position: absolute;
+  top: 0;
+  left: 0;
+  width: 100%;
+  height: 100%;
+  object-fit: cover;
+}
+
+.beforeafter-preview__image--after {
+  clip-path: polygon(0 0, 50% 0, 50% 100%, 0 100%);
+}
+
+.beforeafter-preview__divider {
+  position: absolute;
+  left: 50%;
+  top: 0;
+  bottom: 0;
+  width: 2px;
+  background: white;
+  box-shadow: 0 0 8px rgba(0, 0, 0, 0.3);
+  transform: translateX(-1px);
+}
+
+.beforeafter-preview__caption {
+  padding: 0.75rem;
+  font-size: var(--text-sm);
+  color: var(--color-gray-600);
+  font-style: italic;
+  background: var(--color-background);
+  margin: 0;
+}
+
+.beforeafter-preview__empty {
+  padding: 3rem 1rem;
+  text-align: center;
+  color: var(--color-gray-500);
+  font-size: var(--text-sm);
+}
+
+.beforeafter-preview:hover .beforeafter-preview__images {
+  opacity: 0.9;
+}
+</style>