fix: TLS连接池复用 + 禁言检测 + 降级回复静默

- llm/openai.go: 移除DisableKeepAlives，启用连接池(100idle/20perhost/90s)
  修复频繁TLS握手超时问题
- qq/adapter.go: 监听group_ban通知，发送前检查禁言状态
  防止向被禁言群发消息导致风控
- cmd/main.go: 降级回复仅管理员私聊，群聊静默失败避免怪话
- protocol.go: OBv11Message新增Duration字段
- bridge/router.go: 处理noticeToUnified返回nil(内部消费的通知)

backend/platform-bridge/cmd/main.go

@@ -442,10 +442,23 @@ func startOBv11Readers(router *bridge.PlatformRouter) {
 						fmt.Printf("[qq:%s] route error: %v\n", adapterKey, err)
 						continue
 					}
+					// nil response = internally handled (e.g., mute tracking), skip sending.
+					if response == nil {
+						continue
+					}
 					if response != nil && len(response.Messages) > 0 && !hasOnlySilentMessages(response.Messages) {
 						messageType := msg.MessageType
 						userID := msg.UserID
 						groupID := msg.GroupID
+						// 检查群禁言状态，避免向被禁言的群发送消息导致风控
+						if messageType == "group" {
+							if cur, err := router.GetAdapter(adapterKey); err == nil {
+								if qa, ok := cur.(*qqadapter.Adapter); ok && qa.IsGroupMuted(groupID) {
+									fmt.Printf("[qq:%s] 群 %d 处于禁言状态，跳过发送\n", adapterKey, groupID)
+									continue
+								}
+							}
+						}
 						// Filter non-empty messages and strip 【不发送】 self-censored ones.
 						var toSend []bridge.ResponseMessage
 						for _, rm := range response.Messages {