feat(sync): add converters from Hiboutik DTOs to Prisma inputs

Includes helpers for Hiboutik dates ("0000-00-00" is ignored) and optional prices ("0.00" means no value).

src/utils/price.ts

@@ -0,0 +1,10 @@
+/**
+ * Parses an optional Hiboutik price (discount price, size price override).
+ * Hiboutik sends "0.00" when the value is not set: returns null for empty, zero or invalid values.
+ */
+export function parseOptionalHiboutikPrice(value: string | null | undefined): string | null {
+  if (!value) return null;
+
+  const price = Number(value);
+  return Number.isFinite(price) && price > 0 ? value : null;
+}