test(domain): only a clean PDF diploma is stored and unblocks beoordeling (refs #192)

Red: ProvideDocuments takes the new IDocumentScanner port but ignores it, so
infected, non-PDF and scanner-unavailable uploads are still Accepted.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

tests/acceptance/Support/InMemoryDomainPorts.cs

@@ -77,6 +77,13 @@ public sealed class InMemoryAclClient : IAclClient
     }
 }
 
+/// <summary>A scanner stand-in that returns the verdict the scenario names (S-29) — the live clamd
+/// INSTREAM scan is verified by verify-clamav.</summary>
+public sealed class InMemoryDocumentScanner(ScanVerdict verdict) : IDocumentScanner
+{
+    public Task<ScanVerdict> ScanAsync(byte[] content, CancellationToken ct = default) => Task.FromResult(verdict);
+}
+
 /// <summary>An in-memory user-task client for the beoordeling acceptance scenario: it holds one open
 /// Beoordelen task per registration and records the besluit each is completed with.</summary>
 public sealed class InMemoryUserTaskClient : IUserTaskClient