One Post model for every visibility, read from notes the way peers write them

Post gains what federation and the Mastodon API need: Visibility (Public,
Unlisted, FollowersOnly, Direct, Circle, LocalGeo), the author's account
id, to/cc, the Create's id, url, context, quote, InReplyToURI and the
parent's author, a separate SpoilerText next to the title, language,
mentions, hashtags, remote attachments (alt text, blurhash, focus, size),
reply/favourite/reblog counters, revisions, EditedAt and DeletedAt.

Direct messages are Posts with Visibility Direct and a ConversationId;
migration _005 copies DmPost rows across with their ids and fills the new
fields of existing posts. DmPost is left in place so a rollback still sees
the old messages.

Inbound:
- NoteParser reads Note, Article, Page, Question and media types: content,
  then contentMap, then _misskey_content; summary as the spoiler and name
  as the title; Mention and Hashtag tags; attachments; a PeerTube-style
  list attribution prefers the person over the channel; quote URIs.
- Addressing classifies like Mastodon, finding followers-only by the
  author's own followers URL (now stored on ForeignAvatar), not by a
  "/followers" suffix.
- Create keeps a post when a local persona is addressed or mentioned, when
  it replies to a local post (the parent's reply count goes up) or when a
  community it follows is addressed; an unsolicited public post is not
  stored. Update keeps the previous version as a revision.

The outbox and object endpoints serve only Public and Unlisted posts.

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

PrivaPub/Federation/Objects/Addressing.cs

@@ -0,0 +1,22 @@
+using PrivaPub.Models.Post;
+
+namespace PrivaPub.Federation.Objects
+{
+	public static class Addressing
+	{
+		public const string Public = "https://www.w3.org/ns/activitystreams#Public";
+
+		public static bool IsPublic(string address) => address is Public or "as:Public" or "Public";
+
+		public static PostVisibility Classify(IReadOnlyCollection<string> to, IReadOnlyCollection<string> cc, string authorFollowers)
+		{
+			if (to.Any(IsPublic))
+				return PostVisibility.Public;
+			if (cc.Any(IsPublic))
+				return PostVisibility.Unlisted;
+			if (!string.IsNullOrEmpty(authorFollowers) && (to.Contains(authorFollowers) || cc.Contains(authorFollowers)))
+				return PostVisibility.FollowersOnly;
+			return PostVisibility.Direct;
+		}
+	}
+}