连续签到：断签当天归零重计

-- 错误：按"日"数字相减，跨月出负数
local day = tonumber(os.date("%d"))
local last = tonumber(getplayvar(p, "signDay") or "1")
local add = day - last

local function doSign(p)
    local today = os.date("%Y%m%d")
    local yday = os.date("%Y%m%d", os.time() - 86400)
    if getplayvar(p, "signDate") == today then
        sendmsg(p, 1, "今日已签到")
        return
    end
    local n = 1
    if getplayvar(p, "signDate") == yday then
        n = (getplayvar(p, "signN") or 0) + 1
    end
    setplayvar(p, "signDate", today)
    setplayvar(p, "signN", n)
    giveitem(p, 9001 + math.min(n, 7), 1)
    sendmsg(p, 1, "连签 " .. n .. " 天，奖励已发放")
end