M2: every inbox answer is recorded

InboxReceiver records each answer once, in a finally, with a reason: too-large, not-json,
not-activity, missing-type-or-actor, no-signature, the signature check's own codes
(headers-unsigned, digest-mismatch, header-unreadable, date-skew, expired,
algorithm-unsupported), signature-invalid, actor-not-key-owner, key-unavailable,
id-cross-origin, undo-foreign, misattributed, unknown-recipient, and for 202s queued,
duplicate, suspended or self-delete-unknown-key. Each event carries the activity and object
type, the inbox, the signature scheme, the bytes and the time taken. A 404 for an unknown
/mouth and a rate-limited inbox (429, from OnRejected) are recorded too.

Until the signature verifies, the host is only claimed, so it is kept only if the server is
already known. A suspended server is recorded under its own name.

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

PrivaPub/Federation/Controllers/PeasantsController.cs

@@ -248,7 +248,7 @@ namespace PrivaPub.Federation.Controllers
 		{
 			var local = await _localActors.FindByUserName(actor, token);
 			if (local is not { IsFederated: true })
-				return NotFound();
+				return Answer(_inbox.NoSuchRecipient(Request));
 			return Answer(await _inbox.Receive(Request, local, token));
 		}
 
@@ -359,7 +359,7 @@ namespace PrivaPub.Federation.Controllers
 		IActionResult Answer(InboxResult result)
 		{
 			if (result.Error != default)
-				_logger.LogInformation("Inbox refused with {Status}: {Error}", result.StatusCode, result.Error);
+				_logger.LogInformation("Inbox refused with {Status} ({Reason}): {Error}", result.StatusCode, result.Reason, result.Error);
 			if (result.RetryAfterSeconds is { } seconds)
 				Response.Headers.RetryAfter = seconds.ToString(System.Globalization.CultureInfo.InvariantCulture);
 			return result.Error == default ? StatusCode(result.StatusCode) : StatusCode(result.StatusCode, result.Error);