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.

utils/randomTailwindColor.ts

@@ -0,0 +1,29 @@
+type TailwindColorPrefix = "text" | "bg" | "shadow" | "from" | "to" | "via" | "group-hover:shadow" | "group-active:shadow";
+
+type TailwindColorShade = 50 | 100 | 150 | 200 | 300 | 400 | 500 | 600 | 700 | 800 | 900;
+
+export const randomTailwindColor = (rand: number, prefix: TailwindColorPrefix = "bg", shade: TailwindColorShade = 100, suffix = "") => {
+	const tailwindColors = [
+		"red",
+		"orange",
+		"amber",
+		"yellow",
+		"lime",
+		"green",
+		"emerald",
+		"teal",
+		"cyan",
+		"sky",
+		"blue",
+		"indigo",
+		"violet",
+		"purple",
+		"fuchsia",
+		"pink",
+		"rose"
+	];
+
+	const randomColorIndex = rand % tailwindColors.length;
+
+	return `${prefix}-${tailwindColors[randomColorIndex]}-${shade}${suffix}`;
+};