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/DocumentService.Tests.Live.csproj

@@ -0,0 +1,47 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+
+    <IsPackable>false</IsPackable>
+    <IsTestProject>true</IsTestProject>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <None Remove="TestData\Pdfs\pdfWithSwissQRCode.pdf" />
+    <None Remove="TestData\Pdfs\valid.pdf" />
+    <None Remove="TestData\Pdfs\pdfWithMoreThanOneAttachment.pdf" />
+    <None Remove="TestData\Pdfs\encryptedPdf.pdf" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <EmbeddedResource Include="TestData\Pdfs\pdfWithSwissQRCode.pdf" />
+    <EmbeddedResource Include="TestData\Pdfs\valid.pdf" />
+    <EmbeddedResource Include="TestData\Pdfs\pdfWithMoreThanOneAttachment.pdf" />
+    <EmbeddedResource Include="TestData\Pdfs\encryptedPdf.pdf" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="coverlet.collector" Version="6.0.0" />
+    <PackageReference Include="FluentAssertions" Version="7.0.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+  </ItemGroup>
+
+  <ItemGroup>
+    <Using Include="Xunit" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\DocumentService.Client\DocumentService.Client.csproj" />
+    <ProjectReference Include="..\DocumentService.Application\DocumentService.Application.csproj" />
+    <ProjectReference Include="..\DocumentService.Domain\DocumentService.Domain.csproj" />
+  </ItemGroup>
+
+</Project>