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>

lib/widgets/segmented_icon_toggle.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import '../theme/design_tokens.dart';
 
 /// A single icon button that fills with a solid circle when active —
 /// the building block for Drive-style toggle controls. Thin wrapper around
@@ -21,7 +22,7 @@ class ToggleIconButton extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final colorScheme = Theme.of(context).colorScheme;
+    final colors = context.nooColors;
 
     return IconButton(
       isSelected: isSelected,
@@ -33,12 +34,12 @@ class ToggleIconButton extends StatelessWidget {
         shape: const WidgetStatePropertyAll(CircleBorder()),
         foregroundColor: WidgetStateProperty.resolveWith(
           (states) => states.contains(WidgetState.selected)
-              ? colorScheme.onPrimaryContainer
-              : colorScheme.onSurfaceVariant,
+              ? colors.accentText
+              : colors.fg2,
         ),
         backgroundColor: WidgetStateProperty.resolveWith(
           (states) => states.contains(WidgetState.selected)
-              ? colorScheme.primaryContainer
+              ? colors.accentSoft
               : Colors.transparent,
         ),
       ),
@@ -55,12 +56,12 @@ class SegmentedIconGroup extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final colorScheme = Theme.of(context).colorScheme;
+    final colors = context.nooColors;
     return Container(
-      padding: const EdgeInsets.all(2),
+      padding: const EdgeInsets.all(3),
       decoration: BoxDecoration(
-        color: colorScheme.surfaceContainerHigh,
-        borderRadius: BorderRadius.circular(20),
+        color: colors.surface,
+        borderRadius: BorderRadius.circular(NooRadii.pill),
       ),
       child: Row(mainAxisSize: MainAxisSize.min, children: children),
     );