Located posts: local only, rounded, matched against their own radius

A post given a latitude and longitude becomes LocalGeo: its position is
rounded to two decimals (about a kilometre) and stored as a 2dsphere
point, its radius clamped to 1-50 km, and it is local only - no Create,
no delivery, no outbox, never in the Mastodon API or on a profile page.
/clientapi/post/nearby takes the viewer's position for the query only
(it is neither stored nor logged), runs $geoNear and keeps posts within
each post's own radius, minus authors the viewer blocks or mutes. A
located post cannot be direct or in a group.

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

PrivaPub/Infrastructure/Data/Indexes.cs

@@ -21,6 +21,7 @@ namespace PrivaPub.Infrastructure.Data
 			await Plain<Post>(token, p => p.ActorURI);
 			await Plain<Post>(token, p => p.ConversationId, p => p.ID);
 			await Plain<Post>(token, p => p.InReplyToURI);
+			await DB.Default.Index<Post>().Key(p => p.Geo, KeyType.Geo2DSphere).CreateAsync(token);
 
 			await Unique<DmPost>(p => p.ObjectURI, Builders<DmPost>.Filter.Type(p => p.ObjectURI, BsonType.String), token);
 			await Plain<DmPost>(token, p => p.GroupId, p => p.ID);