Remove flutter chat (#26)

Had to squash merge manually as Forgejo was erroring

lib/models/content/create.dart

@@ -0,0 +1,41 @@
+import "package:fast_immutable_collections/fast_immutable_collections.dart";
+import "package:freezed_annotation/freezed_annotation.dart";
+import "package:nexus/models/content/content.dart";
+part "create.freezed.dart";
+part "create.g.dart";
+
+@freezed
+abstract class CreateContent extends Content with _$CreateContent {
+  CreateContent._();
+  factory CreateContent({
+    @JsonKey(name: "creator") String? creatorId,
+
+    @JsonKey(name: "additional_creators")
+    @Default(IList.empty())
+    IList<String> additionalCreatorIds,
+
+    PreviousRoom? predecessor,
+
+    @JsonKey(name: "m.federate") @Default(true) bool federated,
+
+    @Default("1") String roomVersion,
+    @JsonKey(unknownEnumValue: RoomType.room) RoomType? type,
+  }) = _CreateContent;
+
+  factory CreateContent.fromJson(Map<String, Object?> json) =>
+      _$CreateContentFromJson(json);
+}
+
+enum RoomType {
+  room,
+  @JsonValue("m.space")
+  space,
+}
+
+@freezed
+abstract class PreviousRoom with _$PreviousRoom {
+  const factory PreviousRoom({required String roomId}) = _PreviousRoom;
+
+  factory PreviousRoom.fromJson(Map<String, Object?> json) =>
+      _$PreviousRoomFromJson(json);
+}