refactor: Restructure Application layer with vertical slices and AutoMapper

Vertical slice architecture:

  - Move Features/Documents/{UseCase}/ to {UseCase}/Queries/

  - Query + Handler in SAME file (co-located)

  - Validator in separate file (single responsibility)

New structure:

  - ValidatePdf/Queries/ValidatePdfQuery.cs (Query + Handler)

  - ValidatePdf/Queries/ValidatePdfQueryValidator.cs

  - SwissQrCode/Queries/ExtractSwissQrCodeQuery.cs (Query + Handler)

  - SwissQrCode/Queries/ExtractSwissQrCodeQueryValidator.cs

AutoMapper integration:

  - Add Common/Mapping/MappingProfile.cs

  - Map PdfMetadata -> PdfValidationResult (domain -> DTO)

  - Map SwissQrCodeData -> SwissQrCodeExtractionResult (domain -> DTO)

  - Controllers now thin: pass request to MediatR, AutoMapper handles mapping

DTO improvements:

  - Rename: ValidatePdfResponse -> PdfValidationResult (business-friendly)

  - Rename: ExtractSwissQrCodeResponse -> SwissQrCodeExtractionResult

  - Support BOTH byte[] and Base64Pdf string (XOR validation)

  - Use modern C# 12 collection expressions

Code quality:

  - Use PascalCase for primary constructor parameters

  - Fix LoggingBehavior logging format

Deleted old structure:

  - Features/Documents/ValidatePdf/ (old horizontal structure)

  - Features/Documents/ExtractSwissQrCode/ (old horizontal structure)

  - Common/DTOs/{Request|Response} (replaced with {Result})

Result: Vertical slices, AutoMapper v16.2.0, thin controllers

DocumentOperator.Application/ValidatePdf/Queries/ValidatePdfQuery.cs

@@ -0,0 +1,45 @@
+using AutoMapper;
+using DocumentOperator.Application.Common.DTOs;
+using DocumentOperator.Application.Common.Interfaces;
+using MediatR;
+
+namespace DocumentOperator.Application.ValidatePdf.Queries;
+
+/// <summary>
+/// Query for PDF validation (supports both byte array and Base64 input)
+/// </summary>
+public record ValidatePdfQuery : IRequest<PdfValidationResult>
+{
+    /// <summary>
+    /// PDF as byte array (direct upload)
+    /// </summary>
+    public byte[]? PdfBytes { get; init; }
+
+    /// <summary>
+    /// PDF as Base64 string (API clients)
+    /// </summary>
+    public string? Base64Pdf { get; init; }
+}
+
+/// <summary>
+/// Handler for ValidatePdfQuery
+/// Orchestrates PDF validation using IPdfProcessor and AutoMapper
+/// </summary>
+public class ValidatePdfQueryHandler(IPdfProcessor PdfProcessor, IMapper Mapper) 
+    : IRequestHandler<ValidatePdfQuery, PdfValidationResult>
+{
+    /// <summary>
+    /// Validates PDF and returns metadata
+    /// </summary>
+    public async Task<PdfValidationResult> Handle(ValidatePdfQuery request, CancellationToken cancellationToken)
+    {
+        // Use byte[] if available, otherwise convert Base64
+        byte[] pdfBytes = request.PdfBytes ?? Convert.FromBase64String(request.Base64Pdf!);
+
+        // Call DevExpress service (can throw PdfProcessingException)
+        var metadata = await PdfProcessor.ValidateAsync(pdfBytes);
+
+        // Map domain entity to DTO using AutoMapper
+        return Mapper.Map<PdfValidationResult>(metadata);
+    }
+}

DocumentOperator.Application/ValidatePdf/Queries/ValidatePdfQueryValidator.cs

@@ -0,0 +1,59 @@
+using DocumentOperator.Application.ValidatePdf.Queries;
+using FluentValidation;
+
+namespace DocumentOperator.Application.ValidatePdf.Queries;
+
+/// <summary>
+/// Validator for ValidatePdfQuery
+/// Ensures exactly ONE input method is provided (either PdfBytes OR Base64Pdf, not both, not none)
+/// </summary>
+public class ValidatePdfQueryValidator : AbstractValidator<ValidatePdfQuery>
+{
+    public ValidatePdfQueryValidator()
+    {
+        RuleFor(x => x)
+            .Must(HasExactlyOneInput)
+            .WithMessage("Either PdfBytes or Base64Pdf must be provided, but not both");
+
+        // Validate Base64 format if provided
+        When(x => !string.IsNullOrWhiteSpace(x.Base64Pdf), () =>
+        {
+            RuleFor(x => x.Base64Pdf)
+                .Must(BeValidBase64)
+                .WithMessage("Invalid Base64 format");
+        });
+
+        // Validate byte array if provided
+        When(x => x.PdfBytes != null, () =>
+        {
+            RuleFor(x => x.PdfBytes)
+                .NotEmpty()
+                .WithMessage("PdfBytes cannot be empty");
+        });
+    }
+
+    private static bool HasExactlyOneInput(ValidatePdfQuery request)
+    {
+        var hasPdfBytes = request.PdfBytes != null && request.PdfBytes.Length > 0;
+        var hasBase64 = !string.IsNullOrWhiteSpace(request.Base64Pdf);
+
+        // XOR: exactly one must be true
+        return hasPdfBytes ^ hasBase64;
+    }
+
+    private static bool BeValidBase64(string? base64)
+    {
+        if (string.IsNullOrWhiteSpace(base64))
+            return false;
+
+        try
+        {
+            Convert.FromBase64String(base64);
+            return true;
+        }
+        catch (FormatException)
+        {
+            return false;
+        }
+    }
+}