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/noo/lists/noo_banner.dart

@@ -0,0 +1,56 @@
+import 'package:flutter/material.dart';
+import 'package:lucide_icons_flutter/lucide_icons.dart';
+import '../../../theme/design_tokens.dart';
+
+/// Inline info card with an optional text action, e.g. Trash's retention
+/// notice + "Empty trash" (Noo Design System project,
+/// `components/lists/Banner.jsx`, mobile variant).
+class NooBanner extends StatelessWidget {
+  final IconData icon;
+  final Widget child;
+  final String? actionLabel;
+  final VoidCallback? onAction;
+  final bool actionIsDanger;
+
+  const NooBanner({
+    super.key,
+    this.icon = LucideIcons.info,
+    required this.child,
+    this.actionLabel,
+    this.onAction,
+    this.actionIsDanger = true,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    final colors = context.nooColors;
+    return Container(
+      padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 14),
+      decoration: BoxDecoration(color: colors.surface, borderRadius: BorderRadius.circular(NooRadii.card)),
+      child: Row(
+        crossAxisAlignment: CrossAxisAlignment.center,
+        children: [
+          Icon(icon, size: 20, color: colors.fg2),
+          const SizedBox(width: 12),
+          Expanded(
+            child: DefaultTextStyle(
+              style: NooText.body.copyWith(color: colors.fg2),
+              child: child,
+            ),
+          ),
+          if (actionLabel != null)
+            GestureDetector(
+              onTap: onAction,
+              child: Text(
+                actionLabel!,
+                style: NooText.buttonSm.copyWith(
+                  fontSize: 14,
+                  color: actionIsDanger ? colors.danger : colors.accentText,
+                ),
+              ),
+            ),
+        ],
+      ),
+    );
+  }
+}