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>

tscn_s/barrel_simple.gd

@@ -1,23 +1,41 @@
-extends StaticBody3D 
+extends StaticBody3D
+## A smashable lobby barrel. Joins the &"barrel" group so the HUD can tally how many
+## remain and fire the "cleared the lobby" reward once the last one bursts.
+
+signal destroyed
+
 # Preload the broken barrel scene
 const BARREL_BROKEN_SCENE = preload("res://tscn_s/BarrelBroken.tscn")
 
+var _destroyed := false
+
+
+func _ready() -> void:
+	add_to_group(&"barrel")
+
+
 func destroy_barrel():
+	# Guard against a double hit in the same frame counting the same barrel twice.
+	if _destroyed:
+		return
+	_destroyed = true
+
 	# 1. Instantiate the broken pieces
 	var broken_instance = BARREL_BROKEN_SCENE.instantiate()
-	
+
 	# 2. Place the fragments exactly where the intact barrel currently is
 	broken_instance.global_transform = self.global_transform
-	
+
 	# 3. Add the fragments to the main game tree
 	get_parent().add_child(broken_instance)
-	
+
 	# 4. (Optional) Apply a physics push to the fragments if you want an explosive effect
 	for child in broken_instance.get_children():
 		if child is RigidBody3D:
 			# Pushes pieces slightly outward and upward
 			var random_direction = Vector3(randf_range(-1, 1), randf_range(0.5, 1.5), randf_range(-1, 1)).normalized()
-			child.apply_central_impulse(random_direction * 5.0) 
-			
-	# 5. Delete the intact barrel
+			child.apply_central_impulse(random_direction * 5.0)
+
+	# 5. Announce the smash (the HUD counts down remaining barrels) and remove the barrel
+	destroyed.emit()
 	queue_free()