pub(crate) fn change_need(edit: &str) -> StringExpand description
A day’s block changed, that day only, as the page asks (JSON: its date,
“2026-10-07”, today when none, and sioul_core::needs::DayEdit: key,
action, from, to…; Needs::change_day). The plan and the page follow;
a block moved is not said again: moving it never brings a nag. Returns
what went wrong, else “”.