Introduced `UserPreferencesDto` to represent UI preferences,
including theme, dark mode, and grid layouts. Added the
`IUserPreferencesService` interface and implemented it in
`UserPreferencesService` to manage preferences stored in
the distributed cache (`dbo.TBDD_CACHE`).
Registered `UserPreferencesService` in dependency injection
and added a NuGet reference for `Microsoft.Extensions.Caching.Abstractions`.
Created `UserPreferencesController` with `GET` and `PUT`
endpoints to retrieve and save user preferences. Validated
theme names in the `PUT` endpoint.
Updated `Program.cs` to ensure proper service registration.
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.
