fix(wire): a.gw 在接线 onPersisted 前赋值——防 nil Server panic

wire.go 原在 a.channelBridge.SetOnPersisted(a.gw.BroadcastPersisted) / AuditEvent 之后才
a.gw=gw(663)，导致网关 Server 字段为 nil；一旦有 IM 主人私聊落主会话→notifyPersisted→
BroadcastPersisted(nil receiver)→panic 崩溃，面板 adminBackthink 请求失败显示'暂无后台思考'。
把 a.gw=gw 提前到 gw.SetVoice 后(接线前)，移除冗余复制。go build/test 全绿, 已重建部署.

cmd/cyrene/wire.go

@@ -648,6 +648,7 @@ func (a *app) wireFrontend() error {
 		return fmt.Errorf("gateway: %w", err)
 	}
 	gw.SetVoice(a.voice)
+	a.gw = gw // assign BEFORE wiring hooks below, which capture a.gw / gw (nil-receiver panic otherwise)
 	if a.channelBridge != nil {
 		// Route the channel bridge's owner-private persisted messages into the same
 		// `message_persisted` broadcast the orchestrator uses, so the Web client mirrors
@@ -660,9 +661,9 @@ func (a *app) wireFrontend() error {
 			a.gw.AuditEvent("bridge:"+msg.Platform, "channel.reject", reason)
 		})
 	}
-	a.gw = gw
 	a.capacitySink = gw
 
+
 	// Wire the backthink proactive sinks now that the gateway hub (active-client
 	// route) and the channel bridge (IM fallback) both exist. They were absent when
 	// backthink.New ran (the hub needs the loop and the bridge needs the loop and the