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/Api/Mastodon/Mappers/MastodonMapper.cs

@@ -543,7 +543,12 @@ namespace PrivaPub.Api.Mastodon.Mappers
 			{
 				Name = post.Place.Name, Latitude = post.Place.Latitude, Longitude = post.Place.Longitude, Country = post.Place.Country
 			},
-			Votes = new PrivaPubVotes { Up = post.FavouritesCount, Down = post.DownvotesCount }
+			Votes = new PrivaPubVotes { Up = post.FavouritesCount, Down = post.DownvotesCount },
+			Flairs = post.Flairs?.Select(f => new PrivaPubFlair
+			{
+				Id = f.Id, Name = f.Name, Slug = f.Slug, Description = f.Description, Color = f.Color, TextColor = f.TextColor,
+				BackgroundColor = f.BackgroundColor, BlurImages = f.BlurImages
+			}).ToList() ?? new()
 		};
 
 		PrivaPubVariant Variant(MediaVariant variant) => new()