Communities follow FEP-1b12, circles federate to their members only

Communities:
- a post addressed to a community (to, cc or audience) is accepted
  according to its posting policy - followers, anyone, or moderators -
  and GroupDistributor announces the whole activity with `audience` to
  the community's followers, plus the object for new posts so Mastodon
  shows them; updates and deletes of community content are announced too;
- top-level posts are Pages with a name (the title, or a headline from
  the text); /flock counts members, /wardens lists moderators;
- a Mastodon client posts into a community by mentioning it, or into a
  remote group, which sets `audience`;
- an Announce of an activity from a remote group a persona follows (Lemmy)
  is followed through: the object is fetched from its own origin, kept with
  its AudienceURI, and fanned out to the group's local followers; updates
  are applied in place and deletes checked against the origin.

Circles stop being local-only: an undiscoverable Group actor whose follows
are all requests the owner approves; posts addressed to the circle and its
/flock and delivered to members' own inboxes, never announced, never
public; a remote member's post into the circle is accepted from members
only. SignedFetchAuthorizer serves circle posts and collections only to a
signed request from a member or a member server's instance actor - 404 for
anyone else. Circles never surface in search, lookups, mentions, account
ids or profile pages.

Federation:SecureMode requires a valid signature on every GET under
/peasants except the instance actor. Group forms take a posting policy.

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

PrivaPub/Api/Mastodon/Mappers/MastodonMapper.cs

@@ -6,6 +6,7 @@ using PrivaPub.Domain.Media;
 using PrivaPub.Federation.Actors;
 using PrivaPub.Federation.Rendering;
 using PrivaPub.Models.Federation;
+using PrivaPub.Models.Group;
 using PrivaPub.Models.Post;
 using PrivaPub.Models.Social;
 using PrivaPub.Models.User;
@@ -124,7 +125,7 @@ namespace PrivaPub.Api.Mastodon.Mappers
 
 			foreach (var avatar in await _dbEntities.Avatars.Match(a => wanted.Contains(a.ID) && !a.DeletionAt.HasValue).ExecuteAsync(token))
 				accounts[avatar.ID] = await Local(_localActors.FromAvatar(avatar), false, token);
-			foreach (var group in await _dbEntities.Groups.Match(g => wanted.Contains(g.ID) && !g.DeletionAt.HasValue).ExecuteAsync(token))
+			foreach (var group in await _dbEntities.Groups.Match(g => wanted.Contains(g.ID) && !g.DeletionAt.HasValue && g.Kind == GroupKind.Community).ExecuteAsync(token))
 				accounts[group.ID] = await Local(_localActors.FromGroup(group), false, token);
 			foreach (var foreign in await _dbEntities.ForeignAvatars.Match(f => wanted.Contains(f.ID)).ExecuteAsync(token))
 				accounts[foreign.ID] = Foreign(foreign);