Add Swiss QR Code extraction endpoint

Added a new `/extract-swiss-qr-code` endpoint to extract and parse Swiss QR Codes from the last page of a PDF document. Implemented the `ExtractSwissQrCode` handler method, along with helper methods to map domain value objects (`SwissQrCodeData` and `AddressData`) to DTOs.

Updated `ExceptionHandlingMiddleware` to handle the new `SwissQrCodeNotFoundException` with a 404 Not Found response.

Added integration tests in `ExtractSwissQrCodeEndpointTests` to validate the endpoint's behavior for valid requests, invalid Base64 input, empty references, and empty PDFs. Introduced a helper method to load embedded PDF resources as Base64 strings for testing.

Updated `using` directives to include necessary namespaces for the new feature and exception handling.

DocumentOperator.API/Middleware/ExceptionHandlingMiddleware.cs

@@ -1,4 +1,5 @@
 using DocumentOperator.Domain.Common.Exceptions;
+using DocumentOperator.Domain.Exceptions;
 using FluentValidation;
 using Microsoft.AspNetCore.Mvc;
 using System.Net;
@@ -94,6 +95,19 @@ public class ExceptionHandlingMiddleware
                 }
             ),
 
+            // Swiss QR Code Not Found Exception (404 Not Found)
+            SwissQrCodeNotFoundException qrNotFoundEx => (
+                HttpStatusCode.NotFound,
+                new ProblemDetails
+                {
+                    Type = "https://datatracker.ietf.org/doc/html/rfc7231#section-6.5.4",
+                    Title = "Swiss QR Code Not Found",
+                    Status = (int)HttpStatusCode.NotFound,
+                    Detail = qrNotFoundEx.Message,
+                    Instance = context.Request.Path
+                }
+            ),
+
             // PDF Processing Exception (500 Internal Server Error)
             PdfProcessingException pdfEx => (
                 HttpStatusCode.InternalServerError,