P7: community flairs, from Lemmy and PieFed

- A post's flairs are read in both dialects: Lemmy 1.0's CommunityPostTag (id, slug, name, description, colour slot)
  and PieFed's lemmy:CommunityTag (display name, text and background colours, whether to blur images). Colours are
  kept only as a colour slot or a hex value.
- A community's own list comes from its `tag` and PieFed's older `lemmy:tagsForPosts`, and fills in a post that names
  only a flair's id and slug, as Lemmy's posts do. Edits and refreshes keep them current.
- Clients get them as `privapub.flairs`.

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

PrivaPub/Federation/Inbox/RemoteEdits.cs

@@ -38,6 +38,7 @@ namespace PrivaPub.Federation.Inbox
 			post.Audio = note.Audio ?? post.Audio;
 			post.Event = note.Event ?? post.Event;
 			post.Place = note.Place;
+			post.Flairs = await RemotePosts.Flairs(note, post.AudienceURI, token);
 			if (note.CommentsEnabled is { } enabled)
 				post.LockedAt = enabled ? null : post.LockedAt ?? DateTime.UtcNow;
 			if (!IsEdit(note, post))

PrivaPub/Federation/Inbox/RemotePosts.cs

@@ -137,10 +137,20 @@ namespace PrivaPub.Federation.Inbox
 				EditedAt = note.Updated,
 				Revisions = note.FormerRepresentations.ToList()
 			};
+			post.Flairs = await Flairs(note, post.AudienceURI, token);
 			await Episode(post, note, author, token);
 			return post;
 		}
 
+		// a post's flairs, filled in from its community's list
+		public static async Task<List<PostFlair>> Flairs(NoteDocument note, string communityUri, CancellationToken token)
+		{
+			if (note.Flairs.Count == 0)
+				return default;
+			var community = communityUri == default ? default : await DB.Default.Find<ForeignAvatar>().Match(f => f.ActorURI == communityUri).ExecuteFirstAsync(token);
+			return ObjectShapes.Described(note.Flairs, community?.Flairs);
+		}
+
 		static readonly System.Text.RegularExpressions.Regex Href = new(@"href=""([^""]+)""", System.Text.RegularExpressions.RegexOptions.Compiled);
 
 		// a post that is only a link to a podcast episode of its own author (Castopod announces each episode so): the