feat: complete mobile UI implementation

project/gamescene_test.gd

@@ -4,6 +4,7 @@
 extends SceneTree
 
 const GameScene = preload("res://game_scene.gd")
+const MobileUiRoot = preload("res://ui/mobile/mobile_ui_root.gd")
 
 class FakeClient extends Node:
 	signal entity_spawned(entity: Dictionary)
@@ -122,3 +123,17 @@ func _run() -> void:
 	_ck(true, "points_changed handled without error")
 
 	gs.queue_free()
+	await process_frame
+
+	# Mobile profile uses the same scene assembly and NetPlay HUD contract, but
+	# swaps only the presentation root.  This also guards against accidentally
+	# constructing the desktop HUD alongside the touch layer.
+	ProjectSettings.set_setting("mt/ui/profile", "mobile")
+	var mobile_gs: Node3D = GameScene.new()
+	get_root().add_child(mobile_gs)
+	await mobile_gs.setup(fc, "", "no_such_map")
+	await process_frame
+	_ck(mobile_gs.hud is MobileUiRoot, "mobile profile selects MobileUiRoot")
+	_ck(mobile_gs.hud.input_overlay != null, "mobile profile creates touch overlay")
+	mobile_gs.queue_free()
+	ProjectSettings.set_setting("mt/ui/profile", "auto")