Add MediatR, FluentValidation, AutoMapper, and EF Core

Updated application and infrastructure layers to include MediatR, FluentValidation, AutoMapper, and Entity Framework Core.

- Added new dependencies to `DigitalData.TaskFlow.Application.csproj` and `DigitalData.TaskFlow.Infrastructure.csproj` for MediatR, FluentValidation, AutoMapper, and EF Core.
- Configured MediatR with options and license key support.
- Registered validators and AutoMapper profiles in the application layer.
- Introduced `MediatROptions` and `SwaggerOptions` for configuration.
- Updated `appsettings.json` with connection strings and configuration sections for MediatR and Swagger.
- Replaced placeholder comments in `DependencyInjection` classes with actual service registrations.
- Upgraded `Swashbuckle.AspNetCore` and added `FluentValidation.AspNetCore` for API validation.

src/core/DigitalData.TaskFlow.Application/Options/MediatROptions.cs

@@ -0,0 +1,8 @@
+namespace DigitalData.TaskFlow.Application.Options;
+
+public sealed class MediatROptions
+{
+    public const string SectionName = "MediatR";
+
+    public string? LuckyPennySoftLicenseKey { get; init; }
+}