fix(kook): 丢弃自我回声消息，防 bot 把自己的回复当入站用户消息

KOOK 网关会把 bot 自己发的消息又推回给 bot(author_id=bot uid)，导致 bot 把自己的
回复当成入站用户消息处理(循环/浪费token)。toUnifiedMessage 计算 senderID 后调用
isSelf(senderID) 比对 a.botID(user/me 解析出的 bot 账号 id)，命中即返回 ok=false 丢弃。
- identity.go: 新增 isSelf(并发安全,botMu)
- message.go: self-echo 丢弃 + debug 日志
- message_test.go: TestToUnified_DropsSelfEcho
验收: go build/vet/test ./... 全绿

plugins/channels/kook/message.go

@@ -82,6 +82,12 @@ func (a *Adapter) toUnifiedMessage(data json.RawMessage, frame []byte) (adapter.
 	_ = json.Unmarshal(ev.Extra, &ex)
 
 	senderID, senderName := senderOf(&ev, &ex)
+	// Self-echo: KOOK pushes the bot's own channel messages back to it via the gateway.
+	// Drop them so the bridge never treats the bot's replies as inbound user messages.
+	if a.isSelf(senderID) {
+		a.log.Debug("self message dropped (echo)", "sender_id", senderID, "channel", ev.TargetID)
+		return adapter.UnifiedMessage{}, false
+	}
 	ct, media := messageKind(ev.Type, content)
 	group := channelIsGroup(ev.ChannelType)