test(live): add live API integration test project (DocumentService.Tests.Live)

End-to-end tests that run against a real, deployed API instance to verify that
all controllers respond correctly over HTTP - bypassing WebApplicationFactory.

Project setup:
- Targets net8.0; xUnit 2.9.3 + FluentAssertions 7.0.0
- References DocumentService.Client, Application and Domain as project refs
- Embeds 4 test PDFs as EmbeddedResources:
    valid.pdf, pdfWithSwissQRCode.pdf, pdfWithMoreThanOneAttachment.pdf,
    encryptedPdf.pdf

LiveApiTestBase:
- Base URL defaults to http://172.24.12.39:9393, overridable via
  LIVE_API_BASE_URL env var
- Constructs typed clients (PdfValidationClient, PdfAttachmentClient,
  PdfOperationsClient, SwissQrCodeClient) backed by a single HttpClient
- LoadPdfBytes / LoadPdfStream helpers for EmbeddedResource access

Test coverage per file:
- PdfValidationLiveTests   : Stream + byte[] overloads for validate and
                             validate-pdfa; empty/corrupted inputs assert 4xx/5xx
- PdfAttachmentLiveTests   : check + extract endpoints; stream and byte[] variants
- PdfOperationsLiveTests   : merge and stamp endpoints
- SwissQrCodeLiveTests     : extract Swiss QR bill; invalid content asserts error

Tests are intentionally skipped in CI (no live server); run manually with
the LIVE_API_BASE_URL variable pointing to a running instance.

DocumentService.Tests.Live/LiveApiTestBase.cs

@@ -0,0 +1,64 @@
+using DocumentService.Client.Clients;
+using Microsoft.Extensions.Logging.Abstractions;
+using System.Reflection;
+
+namespace DocumentService.Tests.Live;
+
+/// <summary>
+/// Shared base for all live API tests.
+/// Uses the typed DocumentService.Client classes — no hardcoded routes.
+///
+/// Live API: http://172.24.12.39:9393/
+/// Override via LIVE_API_BASE_URL environment variable if needed.
+/// </summary>
+public abstract class LiveApiTestBase : IDisposable
+{
+    public static readonly string BaseUrl =
+        Environment.GetEnvironmentVariable("LIVE_API_BASE_URL")
+        ?? "http://172.24.12.39:9393";
+
+    protected readonly HttpClient HttpClient;
+
+    // Typed clients (route-free — routes live inside the client implementations)
+    protected readonly PdfValidationClient ValidationClient;
+    protected readonly PdfAttachmentClient AttachmentClient;
+    protected readonly PdfOperationsClient OperationsClient;
+    protected readonly SwissQrCodeClient QrCodeClient;
+
+    protected LiveApiTestBase()
+    {
+        HttpClient = new HttpClient { BaseAddress = new Uri(BaseUrl) };
+
+        ValidationClient = new PdfValidationClient(HttpClient, NullLogger<PdfValidationClient>.Instance);
+        AttachmentClient = new PdfAttachmentClient(HttpClient, NullLogger<PdfAttachmentClient>.Instance);
+        OperationsClient = new PdfOperationsClient(HttpClient, NullLogger<PdfOperationsClient>.Instance);
+        QrCodeClient     = new SwissQrCodeClient(HttpClient, NullLogger<SwissQrCodeClient>.Instance);
+    }
+
+    // ──────────────────────────────────────────────────────────────
+    // Embedded-resource helpers
+    // ──────────────────────────────────────────────────────────────
+
+    protected static byte[] LoadPdfBytes(string fileName)
+    {
+        var assembly = Assembly.GetExecutingAssembly();
+        var resourceName = $"DocumentService.Tests.Live.TestData.Pdfs.{fileName}";
+
+        using var stream = assembly.GetManifestResourceStream(resourceName)
+            ?? throw new FileNotFoundException(
+                $"Embedded resource not found: '{resourceName}'. " +
+                $"Available: {string.Join(", ", assembly.GetManifestResourceNames())}");
+
+        using var ms = new MemoryStream();
+        stream.CopyTo(ms);
+        return ms.ToArray();
+    }
+
+    protected static Stream LoadPdfStream(string fileName)
+    {
+        var bytes = LoadPdfBytes(fileName);
+        return new MemoryStream(bytes);
+    }
+
+    public void Dispose() => HttpClient.Dispose();
+}