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/performance_test.gd

@@ -45,7 +45,7 @@ func _run() -> void:
 		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")
+	var scene_res := load("res://levels/game_shell.tscn")
 	if not scene_res:
 		push_error("performance_test: failed to load scene.tscn")
 		quit(1)