Refactored `AuthService` to introduce a reusable `CreateDefaultClient` method, reducing code duplication. Updated all relevant methods in `AuthService` to use this new method.
Added `CultureService` to manage application culture/localization, including support for setting, getting, and initializing culture from `localStorage` or browser settings.
Introduced `DocReceiverElementService` for retrieving document receiver elements (signatures) and `EnvelopeService` for managing envelope data retrieval with optional filters. Both services include error handling and consistent JSON deserialization.
These changes improve code maintainability, reusability, and adhere to the single responsibility principle.
