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_test.go

@@ -7,6 +7,21 @@ import (
 	"git.yeij.top/AskaEth/Cyrene_v2/internal/channel/adapter"
 )
 
+func TestToUnified_DropsSelfEcho(t *testing.T) {
+	t.Parallel()
+	a := New(Config{BotToken: "x"})
+	a.setBotIdentity(botIdentity{ID: "bot-1", Username: "Cyrene", Nickname: "Cyrene"})
+	// KOOK pushes the bot's own channel message back to it; author_id == bot id.
+	data := json.RawMessage(`{
+		"channel_type":"GROUP","type":1,"target_id":"chan-1","author_id":"bot-1",
+		"content":"咦，亲爱的这是想戳人家哪里呀♪","msg_id":"m-self","msg_timestamp":1700000000000,"nonce":"",
+		"extra":{"type":1,"guild_id":"g-1","mention":[],"author":{"id":"bot-1","username":"Cyrene","nickname":"Cyrene"}}
+	}`)
+	if _, ok := a.toUnifiedMessage(data, nil); ok {
+		t.Fatal("self-echo message should be dropped (ok=false)")
+	}
+}
+
 func TestToUnified_GroupText(t *testing.T) {
 	t.Parallel()
 	a := New(Config{BotToken: "x"})