chore(wip): upgrade dependencies, begin refactor

frontend/lib/domain/README.md

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+# Domain layer
+
+## `entities` - Model definition
+
+Since we follow the repository structure convention, in this folder we purely define data models, without providing any logic. To reduce boilerplate, we use the `freezed` package. This requires some code generation, which means that all model definitions have the following structure:
+```dart
+import 'package:freezed_annotation/freezed_annotation.dart';
+
+// required: associates our `main.dart` with the code generated by Freezed
+part 'main.freezed.dart';
+// optional: Since our Person class is serializable, we must add this line.
+// But if Person was not serializable, we could skip it.
+part 'main.g.dart';
+```
+
+This is required boilerplate for all models. Then, we define the model itself using the `@freezed` annotation:
+```dart
+@freezed
+...
+```
+
+The `*.frozen.dart` and `*.g.dart` are pure boilerplate and should not be touched.
+
+Note that the description of the data will losely follow the capabilities of the backend but does not need to reflect it exactly. That is where the `data` part is for: translating api calls into flutter objects.