T1: tests stop sharing state they don't own

- JobQueue takes an optional scope, so a test's worker leases and reaps only its own jobs.
- The dead-host delivery test runs alone (Exclusive), on its own jobs, and cleans up the
  breaker rows it trips; the breaker has tests of its own on unique hosts.
- Index and migration tests run alone: they drop indexes and rewrite every post.
- DomainBlocks.Load replaces reflection and a database-wide block in tests.
- Harness.Outgoing sees only deliveries queued since the harness started: Peer ports are
  reused within a run, which made the circle test flaky.
- Two pure-logic tests leave Mongo-gated classes, so CI runs them.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ELjqpznMFMNrJoJUj6K5p2

PrivaPub/Federation/Moderation/DomainBlocks.cs

@@ -44,9 +44,11 @@ namespace PrivaPub.Federation.Moderation
 
 		public bool IsSuspended(string host) => Find(host)?.Severity == DomainBlockSeverity.Suspend;
 
-		public async Task Reload(CancellationToken token)
+		public async Task Reload(CancellationToken token) =>
+			Load(await DB.Default.Find<DomainBlock>().ExecuteAsync(token));
+
+		public void Load(IEnumerable<DomainBlock> blocks)
 		{
-			var blocks = await DB.Default.Find<DomainBlock>().ExecuteAsync(token);
 			_blocks = blocks.Where(b => !string.IsNullOrEmpty(b.Domain))
 				.GroupBy(b => Normalise(b.Domain))
 				.ToDictionary(g => g.Key, g => g.First());