- Introduced `validateSignup` endpoint in AuthController for customer number validation during signup.
- Added `healthCheck` method in AuthService to verify service integrations and database connectivity.
- Implemented `getPaymentMethods`, `getPaymentGateways`, and `refreshPaymentMethods` endpoints in InvoicesController for managing user payment options.
- Enhanced InvoicesService with methods to invalidate payment methods cache and improved error handling.
- Updated currency handling across various services and components to reflect JPY as the default currency.
- Added new dependencies in package.json for ESLint configuration.
