The `EmailTemplateDto` class has been changed from a record with positional parameters to a class with explicit properties, including XML documentation and required modifiers for `Name`, `Body`, and `Subject`.
In the `ResetEnvelopeTemplateCommandHandler`, added necessary using directives, modified the constructor to accept an `IRepository<EmailTemplate>`, and updated the `Handle` method to read and update email templates based on the request's ID or type. The static `Default` collection has been renamed to `Defaults` and now uses `EmailTemplateDto`.
- Modified `ResetEnvelopeTemplateCommand` to implement `IRequest`.
- Introduced `ResetEnvelopeTemplateCommandHandler` to handle requests.
- Added a collection of default email templates for notifications.
