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

tests/screenshot_test.gd

@@ -18,7 +18,7 @@ func _run() -> void:
 	DirAccess.make_dir_recursive_absolute(OUTPUT_DIR)
 
 	# Load and switch to the main scene
-	var scene_res := load("res://scene.tscn")
+	var scene_res := load("res://levels/game_shell.tscn")
 	if scene_res == null:
 		push_error("screenshot_test: Failed to load scene.tscn")
 		quit(1)