Adds a Universal Currency group to Game Rules (name, symbol, singular, plural, denomination) with a CurrencyConfig reader in the banking lib that pluralizes labels and prefixes symbols; registers the game_rules migration.
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
