Lobby barrel-smash reward + roll/slam barrel destruction

Bull's boulder roll now homes on and ploughs through lobby barrels, and
the slam shockwave bursts them within its radius. HUD tallies barrels on
load and fires a confetti "WOooOoW!" + two gold bonus HP pips when the
last one breaks; gates open from run state as fights are cleared.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

levels/to_the_arena_level.gd

@@ -1,13 +1,12 @@
 extends Area3D
-
+## Lobby gate into the arena fight. Always open — the arena is the run's first door.
 
 func _ready() -> void:
-	# Connect the signal via code
 	body_entered.connect(_on_body_entered)
 
+
 func _on_body_entered(body: Node3D) -> void:
-	print("Something entered the trigger: ", body.name)
-	# Check if the colliding object is the player
-	if body.is_in_group("player"):
-			#CHANGE TO BEAR LEVEL
-			print("go to arena level")
+	if not body.is_in_group("player"):
+		return
+	Run.choose_level(&"arena")
+	get_tree().change_scene_to_file(Run.active_level().scene_path)