feat(channel-monitor-v2): 接入模式开关、路由门控与依赖注入

注册 admin/user 路由与 feature/mode 守卫，串联 Wire DI 与设置读写，
公开 channel_monitor_mode 与 hide_throughput 等运行时标志。

backend/internal/handler/setting_handler.go

@@ -103,7 +103,9 @@ func (h *SettingHandler) GetPublicSettings(c *gin.Context) {
 		BalanceLowNotifyRechargeURL:      settings.BalanceLowNotifyRechargeURL,
 
 		ChannelMonitorEnabled:                settings.ChannelMonitorEnabled,
+		ChannelMonitorMode:                   settings.ChannelMonitorMode,
 		ChannelMonitorDefaultIntervalSeconds: settings.ChannelMonitorDefaultIntervalSeconds,
+		ChannelMonitorHideThroughput:         settings.ChannelMonitorHideThroughput,
 
 		AvailableChannelsEnabled: settings.AvailableChannelsEnabled,