Add room preview dialog

Closes #79

lib/models/lazy_load_summary.dart

@@ -7,8 +7,9 @@ part "lazy_load_summary.g.dart";
 @Freezed(toJson: false, fromJson: false)
 @JsonSerializable()
 class const LazyLoadSummary({
-  required final IList<String>? heroes,
-  required final int? joinedMemberCount,
+  @JsonKey(name: "m.heroes") required final IList<String>? heroes,
+  @JsonKey(name: "m.joined_member_count") required final int? joinedMemberCount,
+  @JsonKey(name: "m.invited_member_count")
   required final int? invitedMemberCount,
 }) with _$LazyLoadSummary {
   Map<String, Object?> toJson() => _$LazyLoadSummaryToJson(this);