refactor: simplify lobby server architecture and update app metadata

* remove legacy data bridge, RPC, and server bootstrap files
* simplify lobby scene and node hierarchy
* rename lobby UI scene path and update signal handlers
* replace the application icon and configure the boot splash
* add project description and version metadata

scenes/data/multiplayer_data.gd

@@ -0,0 +1,10 @@
+class_name MultiplayerData extends Node
+
+
+@rpc("authority", "reliable")
+func set_multiplayer_active() -> void:
+	pass
+
+@rpc("authority", "call_local", "reliable")
+func set_active_player_id(_id: int) -> void:
+	pass