Pixelfed places: a remote post's own place, shown and never federated again

A Note's `location` that is a Place with coordinates (Pixelfed sends
them as strings) is kept in the new Post.Place and shown as
Status.privapub.place {name, latitude, longitude, country}; an edit
replaces it. An Event's location stays its own `places`, and nothing
renders a place back out. Closes the INTEROP P2 Pixelfed location gap
and the ROADMAP long-tail item.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

PrivaPub/Models/Post/Post.cs

@@ -1,4 +1,4 @@
-using MongoDB.Bson.Serialization.Attributes;
+using MongoDB.Bson.Serialization.Attributes;
 using MongoDB.Entities;
 
 namespace PrivaPub.Models.Post
@@ -39,6 +39,8 @@ namespace PrivaPub.Models.Post
 		[BsonIgnoreIfNull]
 		public EventDetails Event { get; set; }
 		[BsonIgnoreIfNull]
+		public PostPlace Place { get; set; }
+		[BsonIgnoreIfNull]
 		public PostPoll Poll { get; set; }
 		public List<float> Location { get; set; } = new();
 		public float RangeKm { get; set; } = 5.0f;