feat(shopping): formatQuantity-Utility

src/lib/quantity-format.ts

@@ -0,0 +1,7 @@
+export function formatQuantity(q: number | null): string {
+	if (q === null || q === undefined) return '';
+	const rounded = Math.round(q);
+	if (Math.abs(q - rounded) < 0.01) return String(rounded);
+	// auf max. 2 Nachkommastellen, trailing Nullen raus
+	return q.toFixed(2).replace(/\.?0+$/, '');
+}