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/Stepper.vue

@@ -0,0 +1,22 @@
+<template>
+	<ol
+		class="flex items-center justify-between lg:justify-start w-full p-3 space-x-2 text-sm font-medium text-center text-gray-500 bg-white border border-gray-200 rounded-lg shadow-sm sm:text-base sm:p-4 sm:space-x-4 rtl:space-x-reverse"
+	>
+		<Step :number="1" :active="step === 1" :url="step > 1 && step !== 4 ? getCheckoutBaseUrl(1) : undefined" text="E-Mail-Adresse" />
+		<Step :number="2" :active="step === 2" :url="step > 2 && step !== 4 ? getCheckoutBaseUrl(2) : undefined" text="Lieferadresse" />
+		<Step :number="3" :active="step === 3" :url="step > 3 && step !== 4 ? getCheckoutBaseUrl(3) : undefined" text="Bezahlung" />
+		<Step :number="4" :active="step === 4" text="Bestelldetails" />
+	</ol>
+</template>
+
+<script setup lang="ts">
+const checkoutBaseUrl = "/checkout";
+
+defineProps<{
+	step: number;
+}>();
+
+function getCheckoutBaseUrl(step: number) {
+	return `${checkoutBaseUrl}/${step}`;
+}
+</script>