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>

tests/performance_test.gd

@@ -38,6 +38,13 @@ func _run() -> void:
 	if dp:
 		dp.set_value("mat_spawn_count", STRESS_MATADORS)
 
+	# The run now opens in the fightless lobby; force the matador arena so the stress scene
+	# loads with matadors.
+	var run: Node = root.get_node_or_null("/root/Run")
+	if run != null:
+		run.ensure_run()  # build the run first — the shell's own ensure_run would wipe the override
+		run.debug_level_override = run.get_level(&"arena")
+
 	var scene_res := load("res://scene.tscn")
 	if not scene_res:
 		push_error("performance_test: failed to load scene.tscn")