Refactor: Rename SignatureDto to DocReceiverElementDto

Renamed `SignatureDto` to `DocReceiverElementDto` across the codebase to better reflect its purpose as a DTO for document receiver elements.

Updated all references, including:
- `SignatureController.cs`: Changed `doc.Elements` type to `IEnumerable<DocReceiverElementDto>`.
- `DocumentDto.cs`: Updated `Elements` property type.
- `MappingProfile.cs`: Adjusted mappings for the renamed DTO.
- `IDocumentReceiverElementService.cs` and `DocumentReceiverElementService.cs`: Updated interfaces and services to use the new DTO.
- `TestDocumentReceiverElementController.cs`: Updated generic type parameters.

These changes improve clarity, align naming with the domain model, and ensure consistency throughout the application.

EnvelopeGenerator.Application/Common/Dto/MappingProfile.cs

@@ -23,7 +23,7 @@ public class MappingProfile : Profile
     {
         // Entity to DTO mappings
         CreateMap<Config, ConfigDto>();
-        CreateMap<DocReceiverElement, SignatureDto>();
+        CreateMap<DocReceiverElement, DocReceiverElementDto>();
         CreateMap<DocumentStatus, DocumentStatusDto>();
         CreateMap<EmailTemplate, EmailTemplateDto>();
         CreateMap<Envelope, EnvelopeDto>();
@@ -39,7 +39,7 @@ public class MappingProfile : Profile
 
         // DTO to Entity mappings
         CreateMap<ConfigDto, Config>();
-        CreateMap<SignatureDto, DocReceiverElement>();
+        CreateMap<DocReceiverElementDto, DocReceiverElement>();
         CreateMap<DocumentStatusDto, DocumentStatus>();
         CreateMap<EmailTemplateDto, EmailTemplate>();
         CreateMap<EnvelopeDto, Envelope>();