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/settings/settings_dialogs.dart

@@ -0,0 +1,92 @@
+import 'package:flutter/material.dart';
+import '../../providers/session_controller.dart';
+import '../../theme/design_tokens.dart';
+import '../noo/core/noo_button.dart';
+import '../noo/noo_layout.dart';
+import '../noo/overlays/noo_dialog.dart';
+import '../noo/overlays/noo_overlay_header.dart';
+import '../noo/overlays/noo_sheet.dart';
+
+/// Shared by the account card's own quick "Remove account" action and each
+/// row in the saved-accounts list - same confirm/remove/pop-to-root gate
+/// either way (mirrors the pre-rework `_confirmRemoveActive`/
+/// `_AccountsCard._confirmRemove`), just restyled as [showNooDialog]
+/// (desktop) / [showNooSheet] (mobile) instead of an [AlertDialog].
+Future<void> confirmRemoveAccount(
+  BuildContext context,
+  SessionController session, {
+  required String accountId,
+  required String username,
+  required String host,
+  required bool isActive,
+}) async {
+  final hasOtherAccounts = session.accounts.length > 1;
+  final message = isActive && hasOtherAccounts
+      ? 'Remove $username ($host)? Another saved account will become active.'
+      : 'Remove $username ($host)? You can add it again later.';
+
+  var confirmed = false;
+  void cancel() => Navigator.pop(context);
+  void confirm() {
+    confirmed = true;
+    Navigator.pop(context);
+  }
+
+  Widget buttons(NooColors colors) => Row(
+    children: [
+      Expanded(
+        child: NooButton(
+          variant: NooButtonVariant.secondary,
+          size: NooButtonSize.card,
+          fullWidth: true,
+          onTap: cancel,
+          child: const Text('Cancel'),
+        ),
+      ),
+      const SizedBox(width: NooSpace.sm),
+      Expanded(
+        child: NooButton(
+          variant: NooButtonVariant.danger,
+          size: NooButtonSize.card,
+          fullWidth: true,
+          onTap: confirm,
+          child: const Text('Remove'),
+        ),
+      ),
+    ],
+  );
+
+  final colors = context.nooColors;
+  if (NooLayout.isDesktop(context)) {
+    await showNooDialog(
+      context,
+      title: 'Remove account',
+      children: [
+        Text(message, style: NooText.body.copyWith(color: colors.fg2)),
+        buttons(colors),
+      ],
+    );
+  } else {
+    await showNooSheet(
+      context,
+      children: [
+        NooOverlayHeader(title: 'Remove account', onClose: cancel),
+        Text(message, style: NooText.body.copyWith(color: colors.fg2)),
+        buttons(colors),
+      ],
+    );
+  }
+
+  if (!confirmed) return;
+  if (!context.mounted) return;
+  final navigator = Navigator.of(context);
+  await session.removeAccount(accountId);
+  // Only when this was the last saved account does isLoggedIn drop to false
+  // and main.dart swap the root route to LoginView underneath - pop back to
+  // it then, rather than leaving Settings stranded on top. Removing a
+  // non-active account, or falling back to another one, both keep the user
+  // logged in, so Settings should just stay put.
+  if (!session.isLoggedIn) {
+    navigator.popUntil((route) => route.isFirst);
+  }
+}