cmd/systray: add cmd/systray back as a small client/systray wrapper

Updates #1708

Change-Id: Ia101a4a3005adb9118051b3416f5a64a4a45987d
Signed-off-by: Will Norris <will@tailscale.com>

cmd/systray/systray.go

@@ -0,0 +1,15 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build cgo || !darwin
+
+// systray is a minimal Tailscale systray application.
+package main
+
+import (
+	"tailscale.com/client/systray"
+)
+
+func main() {
+	new(systray.Menu).Run()
+}