As the event name suggests,
localplayer_winddown is only fired on the client side (if it even is; can't seem to get it to show up on my listen server). If you want to observe the events that
are fired, set
net_showevents to 2 on the server and watch the server console.
Anyways, since it's not fired on the server, SourceMod has no way to detect such an event.
Off the top of my head, you'll likely either have to track changes on the
IN_ATTACK2 button with
OnPlayerRunCmdPost or
SDKHook_PostThinkPost, or directly hook
CTFMinigun::WindDown() with
DHooks.