Compose buildings from definitions and capabilities

tests/test_animation_continuity.gd

@@ -53,7 +53,7 @@ func _process(delta: float) -> bool:
 			var ship: Node2D = null
 			for b in field.spawned:
 				if is_instance_valid(b) and b.building_type == GameState.BUILDING_MOTHERSHIP:
-					ship = b
+					ship = b.visual
 			if ship == null:
 				print("TEST_ANIMATION_CONTINUITY: FAIL (mothership never spawned)")
 				quit(1)