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.spec.ts

@@ -0,0 +1,11 @@
+import { parseOptionalHiboutikPrice } from './price';
+
+describe('parseOptionalHiboutikPrice', () => {
+  it('keeps a positive price', () => {
+    expect(parseOptionalHiboutikPrice('12.50')).toBe('12.50');
+  });
+
+  it.each(['0.00', '0', '', 'abc', '-1.00', null, undefined])('returns null for %p', (value) => {
+    expect(parseOptionalHiboutikPrice(value)).toBeNull();
+  });
+});