trello.onCardLabelAdded matches Trello’s addLabelToCard action.
automations/watch-trello-card-labels.automation.ts
board as an ID, short link, or URL. Optional static account defaults to the project binding.
Returns a resource event with actionType: "addLabelToCard", required card, label, and board, plus actionId, occurredAt, optional memberCreator, and the complete provider event.