Remove outdated Flutter migration documents and add new technical descriptions and profile repository implementation

- Deleted `next_steps_flutter.md` and `teknisk_beskrivning_flutter.md` files as they were outdated.
- Added new `next_steps_flutter.md` and `teknisk_beskrivning_flutter.md` files with updated migration plans and technical descriptions for the Flutter frontend.
- Implemented `profile_repository.dart` to handle profile data retrieval and updates using the API.

Co-authored-by: Copilot <copilot@github.com>

flutter/.dart_tool/dartpad/web_plugin_registrant.dart

@@ -0,0 +1,18 @@
+// Flutter web plugin registrant file.
+//
+// Generated file. Do not edit.
+//
+
+// @dart = 2.13
+// ignore_for_file: type=lint
+
+import 'package:file_picker/_internal/file_picker_web.dart';
+import 'package:shared_preferences_web/shared_preferences_web.dart';
+import 'package:flutter_web_plugins/flutter_web_plugins.dart';
+
+void registerPlugins([final Registrar? pluginRegistrar]) {
+  final Registrar registrar = pluginRegistrar ?? webPluginRegistrar;
+  FilePickerWeb.registerWith(registrar);
+  SharedPreferencesPlugin.registerWith(registrar);
+  registrar.registerMessageHandler();
+}