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/Step.vue

@@ -0,0 +1,49 @@
+<template>
+	<li :class="{ 'text-black': active, 'text-green-600': isCompleted, 'cursor-pointer hover:text-black group': url }" class="flex">
+		<button class="flex items-center" @click="navigate(url)" :disabled="!url">
+			<!-- Completed step: checkmark -->
+			<span
+				v-if="isCompleted"
+				class="flex items-center justify-center w-6 h-6 me-2 text-xs bg-green-100 text-green-600 rounded-full shrink-0"
+			>
+				<svg class="w-3.5 h-3.5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+					<path stroke-linecap="round" stroke-linejoin="round" stroke-width="3" d="M5 13l4 4L19 7" />
+				</svg>
+			</span>
+			<!-- Current step: filled circle with number -->
+			<span
+				v-else-if="active"
+				class="flex items-center justify-center w-6 h-6 me-2 text-xs font-bold bg-black text-white rounded-full shrink-0"
+			>
+				{{ number }}
+			</span>
+			<!-- Future step: outline circle with number -->
+			<span
+				v-else
+				class="flex items-center justify-center w-6 h-6 me-2 text-xs border-2 border-gray-300 text-gray-400 rounded-full shrink-0"
+			>
+				{{ number }}
+			</span>
+			<span :class="{ 'font-semibold': active, 'hidden lg:block': !active && !isCompleted }" class="group-hover:underline group-hover:underline-offset-4">
+				{{ text }}
+			</span>
+		</button>
+	</li>
+</template>
+
+<script setup lang="ts">
+const props = defineProps<{
+	number: number;
+	active?: boolean;
+	text: string;
+	url?: string;
+}>();
+
+// Step is completed if it has a URL (means we can go back to it)
+const isCompleted = computed(() => Boolean(props.url));
+
+function navigate(url?: string) {
+	if (!url) return;
+	navigateTo(url);
+}
+</script>