P7: feeds read as accounts, and PieFed's post Move

Lemmy 1.0's multi-communities and PieFed's feeds (`type: Feed`) resolve as accounts: the feed's `following` is kept
once a day with its counts, each community in it is read in turn, and `/api/v1/accounts/:id/following` lists them.
Lemmy's feed carries the instance's key and its text in `description`; both are taken as they are. Following a feed
answers 422 until the owner decides how a feed is followed.

A post moved to another community (PieFed's Move{object: post, origin, target}), relayed by the community it leaves,
goes there with its thread; a move into a community we host is not taken.

Checked in the pasture: a Lemmy 1.0 feed and a PieFed feed list their communities (ours among them); a PieFed post moved
from its web code arrives moved, with its comment.

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

PrivaPub/Federation/Actors/ActorDocument.cs

@@ -11,7 +11,7 @@ namespace PrivaPub.Federation.Actors
 
 	public sealed class ActorDocument
 	{
-		static readonly string[] ActorTypes = { "Person", "Service", "Application", "Group", "Organization" };
+		static readonly string[] ActorTypes = { "Person", "Service", "Application", "Group", "Organization", "Feed" };
 
 		public string Id { get; init; }
 		public string Type { get; init; }
@@ -74,7 +74,8 @@ namespace PrivaPub.Federation.Actors
 				Features = ActorFeatures.Detect(root),
 				PreferredUsername = RemoteActorService.Text(root, "preferredUsername"),
 				Name = RemoteActorService.Text(root, "name"),
-				Summary = RemoteActorService.Text(root, "summary"),
+				// (Lemmy's feed keeps its text in `description`)
+				Summary = RemoteActorService.Text(root, "summary") ?? (type == "Feed" ? RemoteActorService.Text(root, "description") : default),
 				Url = RemoteActorService.Text(root, "url") ?? id,
 				Inbox = Origin.Same(inbox, id) ? inbox : default,
 				Outbox = RemoteActorService.Text(root, "outbox"),