Refactor: Rename DocumentOperator to DocumentService

Updated project and solution files to rename and restructure
`DocumentOperator` to `DocumentService`. Modified project
references in `DocumentService.API.csproj`, `DocumentService.Application.csproj`,
and `DocumentService.Infrastructure.csproj` to reflect the new
naming convention. Updated `DocumentService.sln` to remove
old project references, add new ones, and adjust configuration
and nested project mappings accordingly. This change aligns
the project structure with the new naming convention.

DocumentService.Tests/Integration/API/ExtractSwissQrCodeEndpointTests.cs

@@ -0,0 +1,137 @@
+using DocumentService.API.Controllers; // For ExtractSwissQrCodeBase64Request DTO
+using DocumentService.Application.Common.DTOs;
+using FluentAssertions;
+using Microsoft.AspNetCore.Mvc.Testing;
+using System.Net;
+using System.Net.Http.Json;
+using System.Text.Json;
+using Xunit;
+
+namespace DocumentService.Tests.Integration.API;
+
+public sealed class ExtractSwissQrCodeEndpointTests : IClassFixture<WebApplicationFactory<Program>>
+{
+    private readonly HttpClient _client;
+    private readonly JsonSerializerOptions _jsonOptions;
+
+    public ExtractSwissQrCodeEndpointTests(WebApplicationFactory<Program> factory)
+    {
+        _client = factory.CreateClient();
+        _jsonOptions = new JsonSerializerOptions
+        {
+            PropertyNameCaseInsensitive = true
+        };
+    }
+
+    [Fact]
+    public async Task POST_ExtractSwissQrCode_ValidRequest_Returns200()
+    {
+        // Arrange
+        var validPdfBase64 = GetEmbeddedResourceAsBase64("DocumentService.Tests.TestData.Pdfs.valid.pdf");
+
+        var request = new ExtractSwissQrCodeBase64Request
+        {
+            Base64Pdf = validPdfBase64
+        };
+
+        // Act
+        var response = await _client.PostAsJsonAsync("/api/pdf/qr-code/extract-swiss", request);
+
+        // Assert
+        // Note: The test PDF (valid.pdf) may not actually contain a Swiss QR Code
+        // so this test might return 404. We're testing the endpoint wiring here.
+        // A real test would need a PDF with a Swiss QR Code on the last page.
+        response.StatusCode.Should().BeOneOf(HttpStatusCode.OK, HttpStatusCode.NotFound);
+
+        if (response.StatusCode == HttpStatusCode.OK)
+        {
+            var result = await response.Content.ReadFromJsonAsync<SwissQrCodeExtractionResult>(_jsonOptions);
+            result.Should().NotBeNull();
+            result.Bill.Should().NotBeNull();
+            result.RawLines.Should().NotBeEmpty();
+        }
+    }
+
+    [Fact]
+    public async Task POST_ExtractSwissQrCode_InvalidBase64_Returns400()
+    {
+        // Arrange
+        var request = new ExtractSwissQrCodeBase64Request
+        {
+            Base64Pdf = "INVALID_BASE64!!!"
+        };
+
+        // Act
+        var response = await _client.PostAsJsonAsync("/api/pdf/qr-code/extract-swiss", request);
+
+        // Assert
+        response.StatusCode.Should().Be(HttpStatusCode.BadRequest);
+        
+        var problemDetails = await response.Content.ReadAsStringAsync();
+        // FormatException message contains "Base-64" (with hyphen)
+        problemDetails.Should().MatchRegex("(?i)base.?64", "should contain Base64 validation error");
+    }
+
+    [Fact]
+    public async Task POST_ExtractSwissQrCode_NullReferences_AcceptedByValidation()
+    {
+        // Arrange: References are OPTIONAL - null should not cause validation error (400)
+        // Using pdfWithSwissQRCode.pdf which actually has a QR code, so we get 200
+        var validPdfBase64 = GetEmbeddedResourceAsBase64("DocumentService.Tests.TestData.Pdfs.pdfWithSwissQRCode.pdf");
+
+        var request = new
+        {
+            References = (List<string>?)null, // Optional field - should not cause 400
+            Base64Pdf = validPdfBase64
+        };
+
+        // Act
+        var response = await _client.PostAsJsonAsync("/api/pdf/qr-code/extract-swiss", request);
+
+        // Assert: Should NOT be 400 (validation error), should be 200 or 404
+        response.StatusCode.Should().NotBe(HttpStatusCode.BadRequest, 
+            "null References should be accepted (optional field)");
+        
+        // If extraction succeeds, verify empty references array
+        if (response.StatusCode == HttpStatusCode.OK)
+        {
+            var result = await response.Content.ReadFromJsonAsync<SwissQrCodeExtractionResult>();
+            result.Should().NotBeNull();
+        }
+    }
+
+    [Fact]
+    public async Task POST_ExtractSwissQrCode_EmptyPdf_Returns400()
+    {
+        // Arrange
+        var request = new
+        {
+            References = new List<string> { "REF-001" },
+            Base64Pdf = (string?)null
+        };
+
+        // Act
+        var response = await _client.PostAsJsonAsync("/api/pdf/qr-code/extract-swiss", request);
+
+        // Assert
+        response.StatusCode.Should().Be(HttpStatusCode.BadRequest);
+    }
+
+    /// <summary>
+    /// Helper method to load embedded resource as Base64 string
+    /// </summary>
+    private static string GetEmbeddedResourceAsBase64(string resourceName)
+    {
+        var assembly = typeof(ExtractSwissQrCodeEndpointTests).Assembly;
+        using var stream = assembly.GetManifestResourceStream(resourceName);
+
+        if (stream == null)
+        {
+            throw new FileNotFoundException($"Embedded resource not found: {resourceName}");
+        }
+
+        using var memoryStream = new MemoryStream();
+        stream.CopyTo(memoryStream);
+        return Convert.ToBase64String(memoryStream.ToArray());
+    }
+}