feat(ui): add pluralize utility function

Handles irregular plurals, measurement units that stay singular,
and standard English pluralization rules.

src/lib/utils.ts

@@ -4,3 +4,25 @@ import { twMerge } from "tailwind-merge"
 export function cn(...inputs: ClassValue[]) {
   return twMerge(clsx(inputs))
 }
+
+const IRREGULAR: Record<string, string> = {
+  person: "people",
+  child: "children",
+  man: "men",
+  woman: "women",
+};
+
+const NO_PLURAL = new Set([
+  "kg", "g", "mg", "mcg", "l", "ml", "cl", "dl",
+  "m", "cm", "mm", "km", "tick", "hertz", "hz",
+]);
+
+export function pluralize(amount: number, unit: string): string {
+  if (amount === 1) return unit;
+  const lower = unit.toLowerCase();
+  if (NO_PLURAL.has(lower) || unit.endsWith("s")) return unit;
+  if (IRREGULAR[lower]) return IRREGULAR[lower];
+  if (/[^aeiou]y$/i.test(unit)) return unit.slice(0, -1) + "ies";
+  if (/[sxz]$/i.test(unit) || /(sh|ch)$/i.test(unit)) return unit + "es";
+  return unit + "s";
+}