【后端接口】行会建筑：公会大厅的升级与功能解锁

---公会大厅升级：建设度的消耗与等级提升
function Hall.upgrade(actor)
    local player = class(actor)
    if not player then return false end
    local gid = getplayvar(actor, 2, "GuildId")
    if not gid or gid == "" then
        sendmsg(actor, 1, "加入行会后才能捐献")
        return false
    end
    local lv = Hall.levelOf(gid)
    if lv >= 10 then
        sendmsg(actor, 1, "大厅已达最高等级")
        return false
    end
    local need = lv * 10000
    local build = Hall.buildOf(gid)
    if build < need then
        sendmsg(actor, 1, "建设度不足，还需 " .. (need - build))
        return false
    end
    Hall.deductBuild(gid, need)
    Hall.setLevel(gid, lv + 1)
    sendmsg(nil, 1, "「" .. Guild.nameOf(gid) ..
        "」公会大厅升到 " .. (lv + 1) .. " 级！")
    return true
end

---等级权益：功能与等级的映射
local HALL_PERKS = {
    { lv = 1, cap = 50,  repo = 100, skillSlot = 2 },
    { lv = 2, cap = 80,  repo = 150, skillSlot = 3 },
    { lv = 3, cap = 120, repo = 200, skillSlot = 3 },
    { lv = 5, cap = 200, repo = 300, skillSlot = 5 },
}

function Hall.perkOf(gid, field)
    local lv = Hall.levelOf(gid)
    local cfg = HALL_PERKS[lv] or HALL_PERKS[1]
    return cfg[field]
end