/// The `day` value the services API expects: `yyyy-MM-dd`.
///
/// `DateTime.toString()` produces "2026-08-25 00:00:00.000Z", which happens to
/// slip past the backend validator but is not canonical ISO 8601 and differs
/// from what the web sends for the same table.
String serviceDayParam(DateTime d) =>
    '${d.year.toString().padLeft(4, '0')}-'
    '${d.month.toString().padLeft(2, '0')}-'
    '${d.day.toString().padLeft(2, '0')}';