【数据存储】月卡系统：到期标记与每日福利的定时结算

---月卡购买：到期时刻的写入
function MonthCard.buy(actor, days)
    local player = class(actor)
    if not player then return false end
    local expire = tonumber(getplayvar(actor, 2, "CardExpire")) or 0
    -- 未到期的月卡：续费在现有到期日上叠加
    local base = math.max(expire, os.time())
    setplayvar(actor, "HUMAN", "CardExpire",
        base + days * 86400, 1)
    sendmsg(actor, 1, "月卡生效，有效期至 " ..
        os.date('%Y-%m-%d', base + days * 86400))
    return true
end

---每日福利：setday 触发时的定时发放
function setday(actor)
    local player = class(actor)
    if not player then return end
    local expire = tonumber(getplayvar(actor, 2, "CardExpire")) or 0
    if expire > os.time() then
        giveitem(actor, "月卡福利包", 1)
        sendmsg(actor, 1, "月卡每日福利已发放")
    else
        -- 临期提醒：到期前 3 天开始
        local left = math.ceil((expire - os.time()) / 86400)
        if left > 0 and left <= 3 then
            sendmsg(actor, 1, "月卡还剩 " .. left ..
                " 天，续费可享连续特惠")
        end
    end
end