Architecture Refactor

[romandykyi]

This pull request updates NuGet packages and refactors the project structure to include a new layer - Application.

Key changes

• The AdvancedTodoList project was renamed into AdvancedTodoList.WebApp for better clarity.
• A new layer was introduced - Application. It contains the business logic service implementations, DTOs and validators.
• Visual Studio messages and warnings were addresed.
• All NuGet packages were updated.
• Fixed vulnerable NuGet package versions being used in the project.