- Introduced `DomainHttpException` to standardize HTTP error responses with explicit domain error codes.
- Refactored `UnifiedExceptionFilter` to extract detailed exception information, including optional explicit error codes.
- Updated `WhmcsErrorHandlerService` to utilize `DomainHttpException` for better error normalization and handling.
- Removed deprecated error pattern matching logic to enforce explicit error codes in the system.
- Enhanced logging in `WhmcsHttpClientService` to differentiate between expected business outcomes and actual errors.