【界面UI】聊天频道切换：频道分组与未读红点

---频道定义与过滤渲染
local CHANNELS = {
    { key = "world",  name = "世界", color = "#FFFFFF" },
    { key = "guild",  name = "行会", color = "#88DDFF" },
    { key = "team",   name = "队伍", color = "#88FF88" },
    { key = "system", name = "系统", color = "#FFDD44" },
}
ChatUI.current = "world"

function ChatUI.switch(key)
    ChatUI.current = key
    ChatUI.clearLines()
    local lines = ChatUI.buffer[key] or {}
    for _, line in ipairs(lines) do
        ChatUI.append(line.text, line.color)
    end
    ChatUI.unread[key] = 0
    ChatUI.refreshTabs()
end

---后台频道的未读计数
function ChatUI.onMessage(ch, text)
    ChatUI.buffer[ch][#ChatUI.buffer[ch] + 1] =
        { text = text, color = CHANNELS.colorOf(ch) }
    if #ChatUI.buffer[ch] > 200 then
        table.remove(ChatUI.buffer[ch], 1)
    end
    if ch ~= ChatUI.current then
        ChatUI.unread[ch] = (ChatUI.unread[ch] or 0) + 1
        ChatUI.refreshTabs()
    end
end

---页签的红点渲染
function ChatUI.refreshTabs()
    for _, ch in ipairs(CHANNELS) do
        local n = ChatUI.unread[ch.key] or 0
        local tip = n > 0 and ("(" .. n .. ")") or ""
        GUI:Text_setString(ChatUI.tabs[ch.key], ch.name .. tip)
    end
end