Add Swiss QR Code extraction feature

Introduced DTOs for request and response to handle Swiss QR Code extraction from PDF documents. Implemented `ExtractSwissQrCodeHandler` to process the extraction using `ISwissQrCodeProcessor`. Added validation for the query with `ExtractSwissQrCodeValidator`. Developed unit tests to ensure correct behavior for successful and failure scenarios.

DocumentOperator.Application/Common/DTOs/ExtractSwissQrCodeRequest.cs

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+namespace DocumentOperator.Application.Common.DTOs;
+
+/// <summary>
+/// Request to extract Swiss QR Code from a PDF document.
+/// The QR code must be located on the last page of the document.
+/// </summary>
+/// <param name="References">Array of reference strings to pass through in the response</param>
+/// <param name="Base64Pdf">PDF document encoded as Base64 string</param>
+public record ExtractSwissQrCodeRequest(
+    IReadOnlyList<string> References,
+    string Base64Pdf
+);

DocumentOperator.Application/Common/DTOs/ExtractSwissQrCodeResponse.cs

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+namespace DocumentOperator.Application.Common.DTOs;
+
+/// <summary>
+/// Response containing extracted Swiss QR Code data and passed-through references.
+/// </summary>
+/// <param name="References">Reference strings passed through from the request</param>
+/// <param name="QrCodeData">Parsed Swiss QR Code data from the last page of the PDF</param>
+public record ExtractSwissQrCodeResponse(
+    IReadOnlyList<string> References,
+    SwissQrCodeDataDto QrCodeData
+);
+
+/// <summary>
+/// Swiss QR Code data according to Swiss QR Bill Standard 2.0
+/// </summary>
+public record SwissQrCodeDataDto(
+    string QrType,
+    string Version,
+    string CodingType,
+    string Iban,
+    AddressDataDto Creditor,
+    AddressDataDto? UltimateCreditor,
+    decimal? Amount,
+    string Currency,
+    AddressDataDto? UltimateDebtor,
+    string ReferenceType,
+    string? Reference,
+    string? UnstructuredMessage,
+    string? BillInformation,
+    IReadOnlyList<string>? AlternativeProcedureParameters
+);
+
+/// <summary>
+/// Address data (creditor or debtor) in Swiss QR Code
+/// </summary>
+public record AddressDataDto(
+    string AddressType,
+    string Name,
+    string? Street,
+    string? BuildingNumber,
+    string? AddressLine1,
+    string? AddressLine2,
+    string PostalCode,
+    string City,
+    string Country
+);

DocumentOperator.Application/Features/Documents/ExtractSwissQrCode/ExtractSwissQrCodeHandler.cs

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+using DocumentOperator.Application.Common.Interfaces;
+using MediatR;
+
+namespace DocumentOperator.Application.Features.Documents.ExtractSwissQrCode;
+
+/// <summary>
+/// Handles extraction of Swiss QR Code from PDF documents.
+/// Uses ISwissQrCodeProcessor to extract QR code from the last page and parse it.
+/// </summary>
+public sealed class ExtractSwissQrCodeHandler : IRequestHandler<ExtractSwissQrCodeQuery, ExtractSwissQrCodeResult>
+{
+    private readonly ISwissQrCodeProcessor _qrCodeProcessor;
+
+    public ExtractSwissQrCodeHandler(ISwissQrCodeProcessor qrCodeProcessor)
+    {
+        _qrCodeProcessor = qrCodeProcessor;
+    }
+
+    public async Task<ExtractSwissQrCodeResult> Handle(ExtractSwissQrCodeQuery request, CancellationToken cancellationToken)
+    {
+        // Convert Base64 string to byte array
+        byte[] pdfBytes = request.PdfContent.ToByteArray();
+
+        // Extract and parse Swiss QR Code from last page
+        var qrCodeData = await _qrCodeProcessor.ExtractSwissQrCodeAsync(pdfBytes, cancellationToken);
+
+        // Return references (passed through) + QR code data
+        return new ExtractSwissQrCodeResult(
+            References: request.References,
+            QrCodeData: qrCodeData
+        );
+    }
+}

DocumentOperator.Application/Features/Documents/ExtractSwissQrCode/ExtractSwissQrCodeQuery.cs

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+using DocumentOperator.Domain.Models.ValueObjects;
+using DocumentOperator.Domain.ValueObjects;
+using MediatR;
+
+namespace DocumentOperator.Application.Features.Documents.ExtractSwissQrCode;
+
+/// <summary>
+/// Query to extract Swiss QR Code data from a PDF document.
+/// Returns references (passed through) and parsed QR code data.
+/// </summary>
+/// <param name="References">Array of reference strings to pass through in the response</param>
+/// <param name="PdfContent">PDF document content as Base64 string</param>
+public record ExtractSwissQrCodeQuery(
+    IReadOnlyList<string> References,
+    Base64String PdfContent
+) : IRequest<ExtractSwissQrCodeResult>;
+
+/// <summary>
+/// Result containing passed-through references and extracted Swiss QR Code data
+/// </summary>
+/// <param name="References">Reference strings passed through from request</param>
+/// <param name="QrCodeData">Parsed Swiss QR Code data from the last page of the PDF</param>
+public record ExtractSwissQrCodeResult(
+    IReadOnlyList<string> References,
+    SwissQrCodeData QrCodeData
+);

DocumentOperator.Application/Features/Documents/ExtractSwissQrCode/ExtractSwissQrCodeValidator.cs

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+using FluentValidation;
+
+namespace DocumentOperator.Application.Features.Documents.ExtractSwissQrCode;
+
+/// <summary>
+/// Validates ExtractSwissQrCodeQuery before handler execution.
+/// Ensures references array and PDF content are provided.
+/// </summary>
+public sealed class ExtractSwissQrCodeValidator : AbstractValidator<ExtractSwissQrCodeQuery>
+{
+    public ExtractSwissQrCodeValidator()
+    {
+        RuleFor(x => x.References)
+            .NotNull()
+            .WithMessage("References array is required.");
+
+        RuleFor(x => x.PdfContent)
+            .NotNull()
+            .WithMessage("PDF content is required.");
+    }
+}