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/ValidatePdfHandler.cs

@@ -0,0 +1,33 @@
+using DocumentOperator.Application.Common.Interfaces;
+using DocumentOperator.Domain.Models.ValueObjects;
+using MediatR;
+
+namespace DocumentOperator.Application.Features.Documents.ValidatePdf;
+
+/// <summary>
+/// Handler for ValidatePdfQuery
+/// Orchestrates PDF validation using IPdfProcessor
+/// </summary>
+public class ValidatePdfHandler : IRequestHandler<ValidatePdfQuery, PdfMetadata>
+{
+    private readonly IPdfProcessor _pdfProcessor;
+
+    public ValidatePdfHandler(IPdfProcessor pdfProcessor)
+    {
+        _pdfProcessor = pdfProcessor;
+    }
+
+    /// <summary>
+    /// Validates PDF and returns metadata
+    /// </summary>
+    public async Task<PdfMetadata> Handle(ValidatePdfQuery request, CancellationToken cancellationToken)
+    {
+        // Value Object ? Byte Array
+        byte[] pdfBytes = request.PdfContent.ToByteArray();
+
+        // DevExpress Service aufrufen (kann PdfProcessingException werfen)
+        var metadata = await _pdfProcessor.ValidateAsync(pdfBytes);
+
+        return metadata;
+    }
+}

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

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+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>;

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

@@ -0,0 +1,17 @@
+using FluentValidation;
+
+namespace DocumentOperator.Application.Features.Documents.ValidatePdf;
+
+/// <summary>
+/// Validator for ValidatePdfQuery
+/// Validates that PdfContent is not null (Base64String already validates format in its constructor)
+/// </summary>
+public class ValidatePdfValidator : AbstractValidator<ValidatePdfQuery>
+{
+    public ValidatePdfValidator()
+    {
+        RuleFor(x => x.PdfContent)
+            .NotNull()
+            .WithMessage("PDF content is required");
+    }
+}