Add tentacled boss planet encounter

vfx/LaserBeamEffect.gd

@@ -1,6 +1,8 @@
 class_name LaserBeamEffect
 extends Node2D
 
+const COMBAT_TARGET = preload("res://core/CombatTarget.gd")
+
 # The laser shot itself: the strike and the picture of it, with nothing in it
 # about who fired or why.
 #
@@ -71,11 +73,9 @@ static func fire(world: Node, origin: Vector2, direction: Vector2,
 func _strike(direction: Vector2, damage: int) -> void:
 	hit_count = 0
 	var range_along: float = from.distance_to(to)
-	# Asteroids share the enemies' take_damage() contract, so the beam sweeps
-	# both groups in one pass. Shooting a path clear through a field is a
-	# perfectly good use of a laser, and the ore it leaves behind is the point.
-	for enemy in get_tree().get_nodes_in_group("enemies") \
-			+ get_tree().get_nodes_in_group("asteroids"):
+	# Every attackable composition shares this contract, including opened boss
+	# eyes. Shooting a path through an asteroid field still works unchanged.
+	for enemy in get_tree().get_nodes_in_group(COMBAT_TARGET.GROUP):
 		if not is_instance_valid(enemy) or not (enemy is Node2D):
 			continue
 		var to_enemy: Vector2 = enemy.global_position - from