Add ValidatePDF feature with API, Swagger, and tests

Implemented the ValidatePDF feature end-to-end:
- Added `/api/v1/documents/validate` Minimal API endpoint.
- Introduced centralized ExceptionHandlingMiddleware.
- Configured Swagger with `AddSwaggerDocumentation` extension.
- Enabled XML comments in `DocumentOperator.API.csproj`.
- Updated DTOs with XML comments and added `FileSizeMB`.
- Added integration tests for the ValidatePDF endpoint (3 tests).
- Registered infrastructure services (e.g., `IPdfProcessor`).
- Refactored `Program.cs` to include middleware and endpoints.
- Updated PHASENPLAN.md and ROADMAP.md to reflect progress.
- Cleaned up code and made `Program` accessible for tests.

DocumentOperator.Infrastructure/DependencyInjection.cs

@@ -0,0 +1,22 @@
+using DocumentOperator.Application.Common.Interfaces;
+using DocumentOperator.Infrastructure.Services.PdfProcessing;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace DocumentOperator.Infrastructure;
+
+/// <summary>
+/// Dependency Injection configuration for Infrastructure Layer
+/// </summary>
+public static class DependencyInjection
+{
+    /// <summary>
+    /// Registers Infrastructure Layer services (DevExpress, File Storage, etc.)
+    /// </summary>
+    public static IServiceCollection AddInfrastructure(this IServiceCollection services)
+    {
+        // PDF Processing Service (DevExpress)
+        services.AddScoped<IPdfProcessor, DevExpressPdfProcessor>();
+
+        return services;
+    }
+}