Recommend newCardsPerDay from a deadline (Markdown)

Routine read. Markdown plan. Does not write. recommendedNewCardsPerDay is ceil(remaining / study days), not a default of 20. Call this before create when they have a deadline, and again after bulk card adds. Choose newCardsPerDay with the person for this deck. There is no default of 20. When they have a deadline, call previewDeadlinePlan first: it returns ceil(remaining new cards / study days) as a floor. Weigh study time (more time, a higher number), that deadline floor, and card complexity (tiny facts such as times tables can be higher; a beefy card such as the five steps of a cycle must be lower). You may raise N above the floor or negotiate more study time. Send that integer. After bulk card adds, re-run previewDeadlinePlan with that deckId and consider applyDeadlinePlan or updateDeck. 0 introduces no new cards unless the caller asks for extras.