【引擎触发】施毒术：中毒 tick 与解毒的完整状态机

-- 技能命中触发：施毒术命中后调用
function QF.PoisonHit(plr, target, poisonType)
    local now = os.time()
    local st = target:GetState("poison")
    if st and st.expireAt > now then
        st.expireAt = now + 15
        st.stack = math.min((st.stack or 1) + 1, 3)
    else
        target:AddState("poison", { expireAt = now + 15, tick = 2, src = plr.id, stack = 1 })
    end
    target:SendMsg("中了" .. (poisonType == "yellow" and "黄毒" or "灰毒"))
    return true
end

function Poison.tick(target)
    local st = target:GetState("poison")
    if not st then return end
    local dmg = 3 * st.stack
    QF_ApplyDamage(st.src, target, dmg, "poison")
    if target:IsDead() then
        QF_CreditKill(st.src, target)
    end
end

function Poison.cure(target)
    target:ClearState("poison")
    target:SendMsg("中毒解除")
end