test(domain): clamd INSTREAM adapter maps replies to scan verdicts (refs #192)

Red: the stub adapter never connects and always answers Clean.

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

services/domain/Big.Infrastructure/ClamdDocumentScanner.cs

@@ -0,0 +1,10 @@
+using Big.Application;
+
+namespace Big.Infrastructure;
+
+/// <summary>Scans a document with clamd over its INSTREAM protocol (S-29, ADR-0036).</summary>
+public sealed class ClamdDocumentScanner(ClamAvOptions options) : IDocumentScanner
+{
+    public Task<ScanVerdict> ScanAsync(byte[] content, CancellationToken ct = default)
+        => Task.FromResult(ScanVerdict.Clean);
+}

services/domain/Big.Infrastructure/Options.cs

@@ -27,3 +27,12 @@ public sealed class AclOptions
 {
     public Uri BaseUrl { get; set; } = null!;
 }
+
+/// <summary>Where clamd listens (S-29, ADR-0036). <see cref="Timeout"/> bounds one whole scan; a scan that
+/// takes longer counts as the scanner being unavailable.</summary>
+public sealed class ClamAvOptions
+{
+    public string Host { get; set; } = "clamav";
+    public int Port { get; set; } = 3310;
+    public TimeSpan Timeout { get; set; } = TimeSpan.FromSeconds(30);
+}