feat: 公共平台最小化打扰(design/12 §6)——5条策略: 分级+轻思考+限流+审查剔噪

降噪A(策略一/二/五):
- channelbridge/light.go: 非owner分级门——小事件当系统消息登记(不进loop)、非owner轻响应(她判断回/不回,规则优先mention/关键词+轻LLM兜底fail-closed静默)
- backthink 触发降噪: SubjectSystemEvent 低价值不唤醒thinking(仅高价值/owner才think), iot/reminder不受影响
- quiet hours: 安静时段非owner无信号静默,被@才回(非硬性静默); config QUIET_START/END_HOUR 单源共用

限流B(策略三/四):
- adapter/flowgate.go: per-adapter 滑窗限流器+总上限+审查剔噪闸门(Admit两连:速率+上限/审查), owner私聊绕过
- channelbridge/flowgate.go: onMessage入站最前挂闸, 超限/被剔不占worker槽; 审查模型NewLLMReviewer复用model.Adapter(仅>80%阈值触发+跨分钟节流,失败回退FIFO,绝不判身份)
- config: ChannelAccount 加 GroupMsgPerMin(默认6)/MsgPerMin/MaxMessages(默认50), CHANNELS_JSON每账号, 向后兼容
- 被剔消息走OnRejected审计不静默丢

main wire接线: 加modelAdapter字段+Review注入(reviewFor nil-safe,无LLM回退FIFO)
全仓 go build/vet/test 绿(53包)+交叉编译, 零新依赖, 前端无涉

cmd/cyrene/channels.go

@@ -110,13 +110,19 @@ type namedAdapter struct {
 	denyGroups  []string
 	allowUsers  []string
 	denyUsers   []string
+	// flow limits (design/12 §6 策略三/四). They are always surfaced through
+	// Config() so the bridge can build a per-account ingress gate; the bridge maps
+	// the zero default to the protective values and a negative value to "off".
+	groupMsgPerMin int
+	msgPerMin      int
+	maxMessages    int
 }
 
 func (n *namedAdapter) Name() string { return n.name }
 
 func (n *namedAdapter) Config() map[string]any {
 	cfg := n.PlatformAdapter.Config()
-	out := make(map[string]any, len(cfg)+4)
+	out := make(map[string]any, len(cfg)+7)
 	for k, v := range cfg {
 		out[k] = v
 	}
@@ -124,6 +130,9 @@ func (n *namedAdapter) Config() map[string]any {
 	out["denyGroups"] = n.denyGroups
 	out["allowUsers"] = n.allowUsers
 	out["denyUsers"] = n.denyUsers
+	out["groupMsgPerMin"] = n.groupMsgPerMin
+	out["msgPerMin"] = n.msgPerMin
+	out["maxMessages"] = n.maxMessages
 	return out
 }
 
@@ -182,6 +191,9 @@ func buildAccountAdapter(platform string, acct config.ChannelAccount, log *slog.
 		denyGroups:      acct.DenyGroups,
 		allowUsers:      acct.AllowUsers,
 		denyUsers:       acct.DenyUsers,
+		groupMsgPerMin:  acct.GroupMsgPerMin,
+		msgPerMin:       acct.MsgPerMin,
+		maxMessages:     acct.MaxMessages,
 	}, nil
 }