game: add hp pickup

scenes/pickups/pickup_hp.gd

@@ -0,0 +1,14 @@
+class_name PickupHP
+extends PickupBase
+
+@export var value: float = 25.0
+
+@onready var collision_shape_2d: CollisionShape2D = $Area2D/CollisionShape2D
+
+
+func pickup() -> void:
+	if not player:
+		push_error("pickup called on %s without player set" % self)
+		return
+	player.take_damage(-value)
+	queue_free()