Home timelines, mention notifications, and threads that fetch their parents

Fanout writes a TimelineEntry for every persona a post should reach: the
author, local followers of a local author, local followers of a remote one,
the members of a direct conversation or a circle. Mastodon's home rules
apply when it is written: a reply shows only to followers of both sides
(or to the one replied to), a reblog only where reblogs are wanted. A
mention of a local persona becomes a Mention notification.

Inbound posts are now also kept when a persona follows their author.

RemotePosts holds what CreateHandler and backfill share: building a Post
from a note, and fetching a public parent the first time a reply to it
arrives, so its author is known (a reply to an unknown or non-public
parent stays out of home timelines). Each fetched ancestor queues a
FetchAncestors job for the next one, up to ten deep.

/clientapi/timeline/home and /clientapi/notifications (with
/notifications/read) page by max_id for the persona's own root only.

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

PrivaPub.Tests/Federation/InboxScenarioTests.cs

@@ -3,6 +3,7 @@ using Microsoft.Extensions.Logging.Abstractions;
 
 using MongoDB.Entities;
 
+using PrivaPub.Domain.Timelines;
 using PrivaPub.Federation.Actors;
 using PrivaPub.Federation.Inbox.Handlers;
 using PrivaPub.Federation.Inbox;
@@ -53,7 +54,7 @@ namespace PrivaPub.Tests.Federation
 			{
 				new FollowHandler(db, _local, remote, delivery),
 				new UndoHandler(db, _local, remote, delivery),
-				new CreateHandler(db, _local, remote, delivery, _blocks),
+				new CreateHandler(db, _local, remote, delivery, _blocks, new Fanout(db), new RemotePosts(db, _local, remote, _blocks, queue)),
 				new DeleteHandler(db, _local, remote, delivery),
 				new UpdateHandler(db, _local, remote)
 			}, NullLogger<InboxProcessor>.Instance);