An account that moves shows where it went

PrivaPub dropped Move as an unknown type and showed no `moved` on accounts.
Now a Move is believed as Mastodon believes it: the moving account sends it
about itself, and the new account, read again from its own server, names it
in alsoKnownAs (now kept on remote accounts). The old account then shows the
new one as `moved` in the Mastodon API. The personas following it keep
following it: following the new account on their behalf would tell another
server about them, so that waits for the owner.

Checked live against GoToSocial (scenarios/moves.sh: an alias, a move, 6
checks).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

PrivaPub/Federation/Actors/ActorDocument.cs

@@ -33,6 +33,7 @@ namespace PrivaPub.Federation.Actors
 		public string IconDescription { get; init; }
 		public string HeaderDescription { get; init; }
 		public string MovedTo { get; init; }
+		public List<string> AlsoKnownAs { get; init; } = new();//the accounts it says it also is (a Move's target names the moved one)
 		public DateTime? Published { get; init; }
 		public List<CustomEmoji> Emojis { get; init; } = new();
 		public Dictionary<string, string> Fields { get; init; } = new();
@@ -41,6 +42,14 @@ namespace PrivaPub.Federation.Actors
 
 		public ActorKey Key(string keyId) => Keys.FirstOrDefault(k => k.Id == keyId);
 
+		// a property of URIs: one, an array of them, or objects carrying an id
+		static List<string> Uris(JsonElement value) => (value.ValueKind == JsonValueKind.Array ? value.EnumerateArray().ToList() : new List<JsonElement> { value })
+			.Select(v => v.ValueKind == JsonValueKind.String ? v.GetString() : RemoteActorService.Text(v, "id"))
+			.Where(v => Uri.TryCreate(v, UriKind.Absolute, out var uri) && uri.Scheme is "https" or "http")
+			.Distinct(StringComparer.Ordinal)
+			.Take(20)
+			.ToList();
+
 		public static ActorDocument Parse(JsonElement root)
 		{
 			if (root.ValueKind != JsonValueKind.Object)
@@ -75,6 +84,7 @@ namespace PrivaPub.Federation.Actors
 				IconDescription = root.TryGetProperty("icon", out var described) ? Alt(described) : default,
 				HeaderDescription = root.TryGetProperty("image", out var headerImage) ? Alt(headerImage) : default,
 				MovedTo = RemoteActorService.Text(root, "movedTo"),
+				AlsoKnownAs = root.TryGetProperty("alsoKnownAs", out var aliases) ? Uris(aliases) : new(),
 				Published = DateTimeOffset.TryParse(RemoteActorService.Text(root, "published"), CultureInfo.InvariantCulture, DateTimeStyles.AssumeUniversal, out var published)
 					? published.UtcDateTime
 					: default(DateTime?),