P6: custom emoji, fuller remote profiles, and polls both ways

- Custom emoji (Emoji tags) on posts, display names, bios and profile fields, at most 64 per object, proxied, in
  Status.emojis and Account.emojis.
- Remote profiles keep their header, profile fields, locked flag, published date, movedTo, indexable, memorial and
  image descriptions (a locked GoToSocial account no longer shows as open).
- Polls: incoming Questions (Mastodon, Misskey, Pleroma, GoToSocial shapes) with counts, voters, end and closed;
  our own polls from the Mastodon API go out as Questions; votes in are counted once per voter and never become
  replies; personas vote on other servers' polls with one Note per choice; counts refresh with an Update at most every
  three minutes; a poll closes on time and tells its voters and its author. GET /api/v1/polls/:id and POST
  /api/v1/polls/:id/votes.
- An Update without a newer `updated` only refreshes poll, video, audio and event details and leaves no revision.

Checked live against GoToSocial: each side's poll reaches the other as a poll and each side's vote is counted.

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

PrivaPub/Federation/Rendering/ActivityPubRenderer.cs

@@ -37,6 +37,7 @@ namespace PrivaPub.Federation.Rendering
 				["discoverable"] = "toot:discoverable",
 				["indexable"] = "toot:indexable",
 				["blurhash"] = "toot:blurhash",
+				["votersCount"] = "toot:votersCount",
 				["focalPoint"] = new JsonObject { ["@container"] = "@list", ["@id"] = "toot:focalPoint" },
 				["schema"] = "http://schema.org#",
 				["PropertyValue"] = "schema:PropertyValue",
@@ -156,6 +157,23 @@ namespace PrivaPub.Federation.Rendering
 			return note;
 		}
 
+		static void AddPoll(JsonObject note, PostPoll poll)
+		{
+			note["type"] = "Question";
+			note[poll.Multiple ? "anyOf" : "oneOf"] = new JsonArray(poll.Options.Select(option => (JsonNode)new JsonObject
+			{
+				["type"] = "Note",
+				["name"] = option.Title,
+				["replies"] = new JsonObject { ["type"] = "Collection", ["totalItems"] = option.Votes }
+			}).ToArray());
+			if (poll.ExpiresAt is { } ends)
+				note["endTime"] = Timestamp(ends);
+			if (poll.ClosedAt is { } closed)
+				note["closed"] = Timestamp(closed);
+			if (poll.VotersCount is { } voters)
+				note["votersCount"] = voters;
+		}
+
 		static string Headline(PostEntity post)
 		{
 			var text = System.Text.RegularExpressions.Regex.Replace(post.ContentHtml ?? post.Text ?? string.Empty, "<[^>]+>", " ");
@@ -192,6 +210,8 @@ namespace PrivaPub.Federation.Rendering
 			};
 			if (!string.IsNullOrEmpty(post.Language))
 				note["contentMap"] = new JsonObject { [post.Language] = content };
+			if (post.Poll is { } poll)
+				AddPoll(note, poll);
 			var attachments = post.Media.Where(m => !string.IsNullOrEmpty(m.URL)).Select(m =>
 			{
 				var attachment = new JsonObject