Refactor message bus and lobby networking flow

* Add local message bus emission with optional argument expansion
* Improve message type validation and callback dispatch
* Simplify lobby match join/disconnect handling
* Move lobby server networking toward an overridable `ServerNetworking` base class
* Update lobby scene to use the dedicated lobby server script
* Remove obsolete window configuration and unused RPC stubs

scenes/screens/lobby_screen/lobby_server.gd

@@ -0,0 +1,19 @@
+class_name Lobbyserver extends ServerNetworking
+
+
+func _ready() -> void:
+	pass
+
+func _process(_delta: float) -> void:
+	pass
+
+
+func server_client_connected(id: int) -> void:
+	Globals.lobby_data.server_client_connected(id)
+
+func server_client_disconnected(id: int) -> void:
+	# NOTE: Wait for clients to fully disconnect...
+	var timer = get_tree().create_timer(1)
+	await timer.timeout
+
+	Globals.lobby_data.server_client_disconnected(id)