Rebuild UI on the Noo design system

Replaces the Material 3 screens with the Noo design system: warm
neutrals, one violet accent, pill controls, Schibsted Grotesk/
Instrument Sans, Lucide icons, no gradients/shadows.

- New lib/widgets/noo/ component kit (core, lists, files, media, nav,
  overlays) plus lib/theme/design_tokens.dart for the color/type/space/
  radius/motion tokens.
- Rebuilt the app shell (top/bottom bars, drawer, desktop sidebar and
  toolbar), every tab (Files/Offline, Photos, Favorites, Recent,
  Activity, Trash, Shares), Settings, the lock and login screens, the
  media viewer, search, the details/share sheets, and the share-upload
  and move/copy destination pickers.
- Added a design canvas (linked from DESIGN_SYSTEM.md) covering the
  screens the spec didn't already describe, with matching Android and
  iOS chrome; wrote up the approved recipes into DESIGN_SYSTEM.md §4.
- Removed now-dead legacy widgets (media_grid_tile, swipeable_item,
  sync_status_badge, selectable_thumbnail) and updated
  architecture.md/styling.md/standards.md to describe the new
  structure and component/testing conventions.
- Added widget tests for the noo/ component kit.

This is a UI-only rework: no provider/model/service behavior changed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

pubspec.yaml

@@ -45,12 +45,13 @@ dependencies:
   dio: ^5.11.1
   path_provider: ^2.1.5
   open_file: ^3.5.10
-  file_saver: ^0.2.14
+  file_saver: ^0.5.0
   video_player: ^2.9.5
-  pdfx: ^2.9.2
+  pdfx: ^2.11.0
   file_picker: ^13.1.0
   share_plus: ^13.3.0
   material_symbols_icons: ^4.2960.0
+  lucide_icons_flutter: ^3.1.20
   shared_preferences: ^2.5.5
   marquee: ^2.3.0
   local_auth: ^2.3.0
@@ -62,20 +63,17 @@ dev_dependencies:
   flutter_test:
     sdk: flutter
 
+  # Drives tool/screenshots.sh (Play Store screenshots against a fake-data
+  # demo server) - dev only, never part of the release build.
+  integration_test:
+    sdk: flutter
+
   # The "flutter_lints" package below contains a set of recommended lints to
   # encourage good coding practices. The lint set provided by the package is
   # activated in the `analysis_options.yaml` file located at the root of your
   # package. See that file for information about deactivating specific lint
   # rules and activating additional ones.
   flutter_lints: ^6.0.0
-  flutter_launcher_icons: ^0.14.4
-
-flutter_launcher_icons:
-  android: true
-  image_path: "assets/icon/app_icon.png"
-  adaptive_icon_background: "assets/icon/app_icon_background.png"
-  adaptive_icon_foreground: "assets/icon/app_icon_foreground.png"
-  adaptive_icon_monochrome: "assets/icon/app_icon_monochrome.png"
 
 # For information on the generic Dart part of this file, see the
 # following page: https://dart.dev/tools/pub/pubspec