Domain blocks: suspend, silence, reject media

DomainBlock (domain, severity, reject-media, public and private comment)
covers the domain and its subdomains. Admins manage them under
/clientapi/admin/domainblocks/{list,insert,delete}; the set is kept in
memory, reloaded on every change and at most five minutes stale.

A suspended domain is refused by FederationHttp.IsAllowed, so nothing is
fetched from it and no job delivers to it, and the inbox drops its
activities with a 202 before fetching any key. Reject-media strips the
attachments of posts from that domain. Silence is recorded for the
timelines and notifications that arrive in P1.2.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012CzABvBkbcFqoHdmi8b9WB

PrivaPub/Models/Federation/DomainBlock.cs

@@ -0,0 +1,21 @@
+using MongoDB.Entities;
+
+namespace PrivaPub.Models.Federation
+{
+	public class DomainBlock : Entity
+	{
+		public string Domain { get; set; }
+		public DomainBlockSeverity Severity { get; set; }
+		public bool RejectMedia { get; set; }
+		public string PublicComment { get; set; }
+		public string PrivateComment { get; set; }
+		public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+	}
+
+	public enum DomainBlockSeverity
+	{
+		None,
+		Silence,
+		Suspend
+	}
+}