fix(agent): 流量上报间隔 60s 改为 10s(第9条)

传统节点由主控秒级轮询,agent 旧默认 60s 才推送一次,所有 agent
入站的流量/在线刷新慢一个数量级(用户真机实证,与具体节点无关)。
defaultTrafficInterval 改为 10s;心跳间隔 60s 不动;注册退避上限
(registrationBackoff 的 60s)与流量无关,不动。原注释称 traffic
piggyback 心跳 tick 与实现不符(实为独立 ticker),一并改正。

internal/agent/agent.go

@@ -26,8 +26,10 @@ const (
 	defaultPollInterval = 30 * time.Second
 	// Heartbeat interval
 	defaultHeartbeatInterval = 60 * time.Second
-	// Traffic report interval (piggybacks the heartbeat tick)
-	defaultTrafficInterval = 60 * time.Second
+	// Traffic report interval (own ticker; 10s keeps agent inbounds'
+	// traffic/onlines freshness in the same order of magnitude as the
+	// master's seconds-level polling of traditional panel nodes)
+	defaultTrafficInterval = 10 * time.Second
 )
 
 // DefaultBinFolder is used when XUI_BIN_FOLDER is unset. It matches the