Complete Step 1.1: ValidatePDF Application Layer

Updated PHASENPLAN and ROADMAP to reflect progress on Feature 1 - ValidatePDF (75% complete). Marked Step 1.1 as completed, including MediatR setup, pipeline behaviors (`ValidationBehavior`, `LoggingBehavior`), ValidatePDF feature (Query, Handler, Validator), and DTOs.

Added `DependencyInjection.cs` for Application Layer DI configuration. Introduced `LoggingBehavior` and `ValidationBehavior` for MediatR pipelines. Implemented `ValidatePdfHandler`, `ValidatePdfQuery`, and `ValidatePdfValidator`.

Created DTOs (`ValidatePdfRequest`, `ValidatePdfResponse`) for the ValidatePDF feature. Added unit tests for `ValidatePdfHandler` to verify metadata handling and exception propagation.

Removed unused folder references in `DocumentOperator.Application.csproj`.

DocumentOperator.Application/Features/Documents/ValidatePdf/ValidatePdfQuery.cs

@@ -0,0 +1,10 @@
+using DocumentOperator.Domain.Models.ValueObjects;
+using MediatR;
+
+namespace DocumentOperator.Application.Features.Documents.ValidatePdf;
+
+/// <summary>
+/// Query to validate a PDF document and return metadata
+/// </summary>
+/// <param name="PdfContent">PDF content as Base64 string (validated by Value Object)</param>
+public record ValidatePdfQuery(Base64String PdfContent) : IRequest<PdfMetadata>;