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>

Assets/lobby_underground.gd

@@ -1,8 +1,13 @@
 extends Node3D
+## Lobby geometry — watches the run state and raises the bear-gate grid once the arena has
+## been cleared. The DP flag stays as a designer override for testing the animation.
 
 var bear_gate_open := false
 
-func _process(_delta):
-	if DP.b("gate_unlocked_bear") and not bear_gate_open:
+
+func _process(_delta: float) -> void:
+	if bear_gate_open:
+		return
+	if Run.bear_gate_open() or DP.b("gate_unlocked_bear"):
 		bear_gate_open = true
 		$AnimationPlayer.play("Gate_opening")