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.

assets/css/main.css

@@ -0,0 +1,24 @@
+@tailwind base;
+@tailwind components;
+@tailwind utilities;
+
+:root {
+	--vc-slide-gap: 0;
+}
+
+html,
+body {
+	@apply scroll-smooth;
+}
+
+#__nuxt {
+	@apply min-h-screen flex flex-col overflow-x-hidden;
+}
+
+main {
+	@apply flex-grow;
+}
+
+.carousel__slide {
+	@apply pb-0;
+}