The client's JSON comes from generated metadata only

PrivaPub's own types are read through the shared ClientModels context, and a type without generated metadata no longer
falls back to reflection silently: it fails at once in development and on the pasture, and is reported on the console
elsewhere. Startup outside production checks that every PrivaPub and Mastodon type the client knows has its metadata.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01W4YtEJrgxG12Pc39Fai8Bd

MastodonJsonContext.cs

@@ -16,6 +16,7 @@ namespace decePubClient;
 [JsonSerializable(typeof(StatusContext))]
 [JsonSerializable(typeof(Account))]
 [JsonSerializable(typeof(List<Account>))]
+[JsonSerializable(typeof(AccountPage))]
 [JsonSerializable(typeof(Relationship))]
 [JsonSerializable(typeof(List<Relationship>))]
 [JsonSerializable(typeof(List<string>))]