feat: extract shop from mp/shop — initial libreshop/shop

Source moved verbatim from mp/shop/ on 2026-04-29; mp was the first
concrete adapter consuming the libreshop toolkit. Builds and publishes
git.librete.ch/libreshop/shop on every main / v* push via the standard
.gitea/workflows/build.yml shared across libreshop components.

components/PageHero.vue

@@ -0,0 +1,19 @@
+<template>
+	<section class="relative bg-gray-900 text-white py-20 lg:py-32">
+		<div v-if="image" class="absolute inset-0 opacity-30">
+			<img :src="image" :alt="title" class="w-full h-full object-cover" />
+		</div>
+		<div class="relative xl:container mx-auto px-6">
+			<h1 class="text-4xl lg:text-5xl font-bold mb-4">{{ title }}</h1>
+			<p v-if="subtitle" class="text-xl lg:text-2xl text-gray-300 max-w-2xl">{{ subtitle }}</p>
+		</div>
+	</section>
+</template>
+
+<script setup lang="ts">
+defineProps<{
+	title: string;
+	subtitle?: string;
+	image?: string;
+}>();
+</script>