Reorganize into role-based folders and consolidate art

Move every script and scene into role-based directories (actors/, systems/, ui/,
levels/, props/) and all raw art under art/ (grouped by role, snake_case,
Extract-Textures GLBs), dropping Blender version-suffix noise. Filenames are
snake_case (PascalCase reserved for class_name) to avoid case-insensitive
filesystem aliasing on the web/macOS targets. Routes the bull's hits through the
typed DamageEvent pipeline and wires the bull's abilities to the Fx library.
Updates CLAUDE.md's folder-layout overview to match.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CCyaJPTHCH9EDthpf4A5Sj

levels/lobby_underground.gd

@@ -0,0 +1,15 @@
+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: 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")
+		if DP.b("gamepad_vibration"):
+			Input.start_joy_vibration(0, 0.5, .5, 7)