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/tabs/tab_day_groups.dart

@@ -0,0 +1,109 @@
+import 'package:flutter/widgets.dart';
+import 'package:intl/intl.dart';
+import '../../theme/design_tokens.dart';
+
+/// Day-bucketing shared by Recent (Today/Yesterday/This week/Earlier) and
+/// Activity (one group per calendar day) - see `DESIGN_SYSTEM.md` §4.
+
+bool _isSameDay(DateTime a, DateTime b) =>
+    a.year == b.year && a.month == b.month && a.day == b.day;
+
+/// One labelled bucket of [items], already in their original (newest-first)
+/// order.
+class TabDayGroup<T> {
+  final String label;
+  final List<T> items;
+  const TabDayGroup(this.label, this.items);
+}
+
+/// Buckets newest-first [items] into Today / Yesterday / This week /
+/// Earlier. Empty buckets are omitted.
+List<TabDayGroup<T>> groupByRecentBucket<T>(
+  List<T> items,
+  DateTime Function(T item) dateOf,
+) {
+  final now = DateTime.now();
+  final today = DateTime(now.year, now.month, now.day);
+  final yesterday = today.subtract(const Duration(days: 1));
+  // "This week" reaches back 6 days before today (7 days inclusive) -
+  // anything older falls to "Earlier".
+  final weekStart = today.subtract(const Duration(days: 6));
+
+  final todayItems = <T>[];
+  final yesterdayItems = <T>[];
+  final weekItems = <T>[];
+  final earlierItems = <T>[];
+
+  for (final item in items) {
+    final d = dateOf(item);
+    final day = DateTime(d.year, d.month, d.day);
+    if (_isSameDay(day, today)) {
+      todayItems.add(item);
+    } else if (_isSameDay(day, yesterday)) {
+      yesterdayItems.add(item);
+    } else if (!day.isBefore(weekStart)) {
+      weekItems.add(item);
+    } else {
+      earlierItems.add(item);
+    }
+  }
+
+  return [
+    if (todayItems.isNotEmpty) TabDayGroup('Today', todayItems),
+    if (yesterdayItems.isNotEmpty) TabDayGroup('Yesterday', yesterdayItems),
+    if (weekItems.isNotEmpty) TabDayGroup('This week', weekItems),
+    if (earlierItems.isNotEmpty) TabDayGroup('Earlier', earlierItems),
+  ];
+}
+
+/// Buckets newest-first [items] one group per calendar day (Activity's
+/// "feed grouped by day" - unlike [groupByRecentBucket], days past
+/// yesterday each keep their own header rather than folding into "This
+/// week"/"Earlier").
+List<TabDayGroup<T>> groupByCalendarDay<T>(
+  List<T> items,
+  DateTime Function(T item) dateOf,
+) {
+  final now = DateTime.now();
+  final today = DateTime(now.year, now.month, now.day);
+  final yesterday = today.subtract(const Duration(days: 1));
+
+  final order = <DateTime>[];
+  final groups = <DateTime, List<T>>{};
+  for (final item in items) {
+    final d = dateOf(item);
+    final day = DateTime(d.year, d.month, d.day);
+    final bucket = groups.putIfAbsent(day, () {
+      order.add(day);
+      return [];
+    });
+    bucket.add(item);
+  }
+
+  String labelFor(DateTime day) {
+    if (_isSameDay(day, today)) return 'Today';
+    if (_isSameDay(day, yesterday)) return 'Yesterday';
+    return DateFormat.yMMMd().format(day);
+  }
+
+  return [for (final day in order) TabDayGroup(labelFor(day), groups[day]!)];
+}
+
+/// The "Today"/"Yesterday"/... label above a day group - `DESIGN_SYSTEM.md`
+/// §2's grouped-list label style (13/600 fg-2, inset 8px). Standalone
+/// (rather than `NooGroupedList.label`) for Activity, whose items aren't a
+/// `NooGroupedList` card.
+class TabGroupLabel extends StatelessWidget {
+  final String label;
+
+  const TabGroupLabel(this.label, {super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    final colors = context.nooColors;
+    return Padding(
+      padding: const EdgeInsets.fromLTRB(8, 0, 8, 8),
+      child: Text(label, style: NooText.label.copyWith(color: colors.fg2)),
+    );
+  }
+}

lib/widgets/tabs/tab_location.dart

@@ -0,0 +1,10 @@
+/// Turns a full item path plus its own name into a display-friendly parent
+/// folder label - shared by Recent ("action + location") and Trash
+/// ("original location") per `DESIGN_SYSTEM.md` §4.
+String tabLocationLabel(String fullPath, String name) {
+  final folder = fullPath.length >= name.length
+      ? fullPath.substring(0, fullPath.length - name.length)
+      : fullPath;
+  final trimmed = folder.replaceAll(RegExp(r'^/+|/+$'), '');
+  return trimmed.isEmpty ? 'Home' : trimmed;
+}

lib/widgets/tabs/tab_state_slivers.dart

@@ -0,0 +1,96 @@
+import 'package:flutter/material.dart';
+import 'package:lucide_icons_flutter/lucide_icons.dart';
+import '../../theme/design_tokens.dart';
+import '../noo/core/noo_button.dart';
+
+/// Shared loading/error/empty slivers for Recent/Activity/Trash/Shares (and
+/// any future tab shaped like them: a `CustomScrollView` over one flat
+/// list), restyled with noo tokens instead of each screen hand-rolling the
+/// same centered column - see `FilesView`'s identical error/empty layout,
+/// which this mirrors.
+
+/// Centered spinner for a tab's first load (list still empty).
+const Widget tabLoadingSliver = SliverFillRemaining(
+  hasScrollBody: false,
+  child: Center(child: CircularProgressIndicator()),
+);
+
+/// Centered error state: icon, title, message, and a Retry button.
+Widget tabErrorSliver(
+  BuildContext context, {
+  required String title,
+  required String message,
+  required VoidCallback onRetry,
+}) {
+  final colors = context.nooColors;
+  return SliverFillRemaining(
+    hasScrollBody: false,
+    child: Center(
+      child: Padding(
+        padding: const EdgeInsets.all(24),
+        child: Column(
+          mainAxisAlignment: MainAxisAlignment.center,
+          children: [
+            Icon(LucideIcons.circleAlert, size: 56, color: colors.danger),
+            const SizedBox(height: 16),
+            Text(
+              title,
+              textAlign: TextAlign.center,
+              style: NooText.cardTitle.copyWith(color: colors.danger),
+            ),
+            const SizedBox(height: 8),
+            Text(
+              message,
+              textAlign: TextAlign.center,
+              style: NooText.body.copyWith(color: colors.fg3),
+            ),
+            const SizedBox(height: 20),
+            NooButton(
+              variant: NooButtonVariant.secondary,
+              size: NooButtonSize.field,
+              icon: LucideIcons.refreshCw,
+              onTap: onRetry,
+              child: const Text('Retry'),
+            ),
+          ],
+        ),
+      ),
+    ),
+  );
+}
+
+/// Centered empty state: an icon over a message.
+Widget tabEmptySliver(
+  BuildContext context, {
+  required IconData icon,
+  required String message,
+}) {
+  final colors = context.nooColors;
+  return SliverFillRemaining(
+    hasScrollBody: false,
+    child: Center(
+      child: Padding(
+        padding: const EdgeInsets.all(24),
+        child: Column(
+          mainAxisAlignment: MainAxisAlignment.center,
+          children: [
+            Icon(icon, size: 56, color: colors.fg3),
+            const SizedBox(height: 12),
+            Text(
+              message,
+              textAlign: TextAlign.center,
+              style: NooText.cardTitle.copyWith(color: colors.fg2),
+            ),
+          ],
+        ),
+      ),
+    ),
+  );
+}
+
+/// Bottom padding sliver so the last row/card clears the bottom nav/FAB -
+/// same trailing pair every rebuilt tab list ends on.
+const List<Widget> tabBottomInsetSlivers = [
+  SliverToBoxAdapter(child: SizedBox(height: 100)),
+  SliverFillRemaining(hasScrollBody: false, child: SizedBox()),
+];