WIP: feat(ui): Migrate to new UI implementation

AGENTS.md

@@ -17,6 +17,9 @@ Important areas:
 - `lib/app` contains UI screens, BLoC state, widgets, and theme code.
 - `lib/app/widgets` contains shared app-level UI such as the custom desktop
   title bar.
+- `lib/app/design_system` contains presentation-only catalog components.
+- `widgetbook/` is the standalone component-catalog workspace. Stories and
+  fixture data stay in that workspace and import components from the launcher.
 - `lib/features/launcher/domain` contains launcher entities such as sessions,
   manifests, news items, sync status, and exceptions.
 - `lib/features/launcher/application` contains use cases for session restore
@@ -32,26 +35,28 @@ Important areas:
 
 ## Flutter SDK Policy
 
-MoonWell Launcher supports the latest stable Flutter SDK only. Do not introduce
-or rely on FVM-pinned workflows.
-
-If `flutter` is not available after installing or updating Flutter, restart the
-shell and verify PATH with `flutter --version`.
+MoonWell Launcher tracks the latest stable Flutter SDK through FVM. Run all
+Dart and Flutter commands through `fvm` and keep `.fvmrc` on the stable channel.
 
 ## Common Commands
 
 ```powershell
-flutter pub get
-dart run build_runner build --delete-conflicting-outputs
-dart format --set-exit-if-changed .
-flutter analyze
-flutter test
-flutter run -d windows --dart-define=MOONWELL_API_BASE_URL=https://host --dart-define=MOONWELL_APPCAST_URL=https://host/launcher/updates/appcast.xml
-flutter build windows --dart-define=MOONWELL_API_BASE_URL=https://host --dart-define=MOONWELL_APPCAST_URL=https://host/launcher/updates/appcast.xml
+fvm flutter pub get
+fvm dart run build_runner build --delete-conflicting-outputs
+fvm dart format --set-exit-if-changed .
+fvm flutter analyze
+fvm flutter test
+fvm flutter run -d windows --dart-define=MOONWELL_API_BASE_URL=https://host --dart-define=MOONWELL_APPCAST_URL=https://host/launcher/updates/appcast.xml
+fvm flutter build windows --dart-define=MOONWELL_API_BASE_URL=https://host --dart-define=MOONWELL_APPCAST_URL=https://host/launcher/updates/appcast.xml
+cd widgetbook
+fvm flutter pub get
+fvm dart run build_runner build
+fvm flutter run -d windows
 ```
 
 See `docs/linting.md` for the required format, analyze, test, and Lefthook
 pre-commit workflow.
+Follow `docs/widgetbook.md` for all Widgetbook use-case generation.
 
 ## Configuration
 
@@ -102,3 +107,5 @@ or local-only API URLs.
 - Always keep `README.md` and files under `docs/` up-to-date with any
   architecture, setup, API, sync, build, or operational change.
 - Keep documentation links current when files move.
+- Keep catalog widgets presentation-only. Do not call BLoCs, APIs, storage,
+  file pickers, dependency injection, or native window plugins from them.