P7: FEP-268d searchableBy decides what search finds

A remote account's searchableBy, and a post's own, outrank indexable in status search: Public lets anyone find a
public post, the author's followers only those who follow it, anything else nobody but those it already reaches
(their own, named, favourited, bookmarked or boosted posts). Read on actors and posts, kept through edits; PrivaPub
does not emit it.

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

PrivaPub/Models/User/Avatar.cs

@@ -78,6 +78,7 @@ namespace PrivaPub.Models.User
 		public string OutboxURL { get; set; }
 		public string FeaturedURL { get; set; }//featured: the posts it pins
 		public List<PrivaPub.Models.Post.PostFlair> Flairs { get; set; } = new();//a community's labels for its posts
+		public List<string> SearchableBy { get; set; }//FEP-268d, when the account states it: outranks IsIndexable
 		public string ModeratorsURL { get; set; }//a community's attributedTo (Lemmy, PieFed, Mbin): the collection of its moderators
 		public List<AssertionKey> AssertionKeys { get; set; } = new();//its Ed25519 keys (FEP-521a), which prove what it sends (FEP-8b32)
 		public string WallURL { get; set; }//sm:wall (FEP-400e): where others write to it, Smithereen's walls