feat: initial etrelay UDP relay with master heartbeat

diagrams/architecture.puml

@@ -0,0 +1,21 @@
+@startuml
+skinparam shadowing false
+title After: everything goes through the front
+
+actor Player as player
+node "Master\netmaster.net:27950" as master
+
+node "Front (public IP)" {
+  component "etrelay\n0.0.0.0:27960" as relay
+}
+
+node "Home" {
+  component "nginx stream\n<wg-peer>:27960" as nginx
+  component "ET server\n<et-server>:27960" as et
+}
+
+player <--> relay : game traffic
+master <--> relay : heartbeat / getChallenge / getInfo
+relay <--> nginx : WireGuard (wg0)
+nginx <--> et : LAN
+@enduml