One StatusService behind both client APIs, with outbound likes and boosts

Domain/Statuses/StatusService takes a persona, not a root, and is what
/clientapi and the Mastodon API share:
- Publish renders Markdown (clientapi) or plain text (Mastodon clients),
  checks the persona may see the post it replies to, opens or reuses the
  conversation for a direct post from its recipients and mentions, fans
  out and hands the Create to the outbox;
- Edit keeps a revision and sends Update{Note}; Remove soft-deletes and
  returns the post, so a client can delete and redraft;
- Favourite and Reblog work on anything the persona can see and send Like,
  Announce and their Undo to the author (and, for boosts, to followers);
  boosts are refused for anything but public and unlisted posts.

PostsService is now the clientapi wrapper that checks the root owns the
persona. A persona's own boost is a local row: the outbox renders it as
Announce, /grunts/announce-{id} resolves, and object endpoints, profile
pages and NodeInfo skip it. ContentFormat gains Plain.

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

PrivaPub/Models/Post/ContentFormat.cs

@@ -3,6 +3,7 @@ namespace PrivaPub.Models.Post
 	public enum ContentFormat
 	{
 		Markdown,
-		Html
+		Html,
+		Plain
 	}
 }