Added project references to establish dependencies between
the API, Application, Domain, and Infrastructure projects.
Updated `DigitalData.EmailProfiler.Tests.csproj` to include
references to all layers for testing purposes. Fixed a BOM
encoding issue in the test project file. Added xUnit usage
directive to ensure proper test framework integration.
Added a `Worker` class as a hosted background service to log
periodic messages. Updated `DigitalData.EmailProfiler.API.csproj`
to include `UserSecretsId` for secure development storage and
added `Microsoft.Extensions.Hosting` package. Replaced the
`Controllers` folder reference with `Properties`. Updated
`Program.cs` to register the `Worker` service, enable API
exploration, and retain Swagger configuration.
