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/TestData/Pdfs/encryptedPdf.pdf

@@ -0,0 +1,30 @@
+%PDF-1.4
+1 0 obj
+<< /Type /Catalog /Pages 2 0 R >>
+endobj
+
+2 0 obj
+<< /Type /Pages /Kids [3 0 R] /Count 1 >>
+endobj
+
+3 0 obj
+<< /Type /Page /Parent 2 0 R /MediaBox [0 0 612 792] >>
+endobj
+
+4 0 obj
+<< /Filter /Standard /V 2 /R 3 /Length 128 /P -3904 /O (OwnerHash12345678901234567890123456) /U (UserHash12345678901234567890123456) >>
+endobj
+
+xref
+0 5
+0000000000 65535 f 
+0000000009 00000 n 
+0000000058 00000 n 
+0000000115 00000 n 
+0000000206 00000 n 
+
+trailer
+<< /Size 5 /Root 1 0 R /Encrypt 4 0 R >>
+startxref
+370
+%%EOF