【界面UI】技能冷却扇形：径向遮罩与扫描动画

---技能图标 + 圆形冷却遮罩
function SkillCD.build(slot, skillId, cdSeconds)
    local cd = GUI:ProgressTimer_Create(slot.node, "cd_" .. skillId, 0, 0, 22)
    GUI:ProgressTimer_setReverseDirection(cd, 1)
    GUI:ProgressTimer_setPercentage(cd, 100)
    slot.cdNode = cd
    slot.cdTotal = cdSeconds
    return cd
end

---点击施放与冷却推进
function SkillCD.bindCast(slot, skillId)
    GUI:addOnClickEvent(slot.btn, function()
        if slot.cooling then
            SL:ShowSystemTips("技能冷却中")
            return
        end
        slot.cooling = true
        SL:SendNetMsg(MSGID.SKILL_CAST, skillId, 0, 0, "")
        SL:Schedule(0.1, function()
            local left = slot.cdEnd - os.time()
            local pct = math.max(0, left / slot.cdTotal * 100)
            GUI:ProgressTimer_setPercentage(slot.cdNode, pct)
            if left <= 0 then slot.cooling = false end
        end)
    end)
end