Set or clear the entry's due date — when the next step on it is due. Send an ISO date
string to set it, or null to clear it. The board shows it on the card and turns the card
red once the date has passed; the table can sort by it.
Bearer <token>.When the next step on this entry is due, as an ISO date string. null (or an
empty string) clears it.
Typed as a string rather than a Date so that clearing is expressible: TSOA
would reject null for a Date field, and the service parses it either way.
Ok