- scenes/avatar_customization.tscn: script_extense -> script (typo meant
the customization UI script was never actually attached to the scene)
- scripts/avatar/avatar_loadout.gd: add missing class_name AvatarLoadout
(avatar_system.gd references the type everywhere; only this file among
the avatar scripts lacked its class_name)
- scripts/main_menu.gd: _ready() referenced _customize_button/_settings_button/
_quit_button but the @onready vars are named without the leading
underscore