Android: the Notifications settings card is not rendered at all, so there is no way to learn that push doesn't exist

[mewc]

Describe the bug

On Android, Settings shows no Notifications section — not the toggle, not the "Unavailable in this build" row, nothing. Android has no push transport yet (#6092, #7482 both open), which is fine and expected; the bug is that the app is silent about it. An Android user's only way to find out that a locked phone will never alert is to wait a day and notice.

The iOS branch of the same widget already has the right behaviour for this case — it renders a disabled row reading "Push notifications — Unavailable in this build" when the gateway define is empty. Android never reaches that code.

Cause

mobile/lib/features/settings/settings_page/notifications_section.dart:7-10:

Widget build(BuildContext context, WidgetRef ref) {
  if (defaultTargetPlatform != TargetPlatform.iOS) {
    return const SizedBox.shrink();
  }

_NotificationsSection is the only notifications UI in mobile settings (mobile/lib/features/settings/settings_page.dart:219 is its sole use site), so the early return removes the entire surface on Android rather than degrading it.

Steps to reproduce

1. Build and run the Flutter app on Android.
2. Join or create a community.
3. Open Settings.
4. There is no Notifications card between the sections above it and "Remove community".

Expected behavior

The card renders on every platform. On Android it shows a non-interactive row stating that push notifications are not yet supported on Android, ideally linking #6092 so a user can follow or thumbs-up the work rather than filing a duplicate.

Actual behavior

Nothing renders. The absence is indistinguishable from "notifications are on and working".

Suggested fix

Replace the platform early-return with a platform branch that reuses the existing unavailable-row pattern:

if (defaultTargetPlatform != TargetPlatform.iOS) {
  return AppListCard(
    label: 'Notifications',
    verticalPadding: Grid.twelve,
    children: [
      AppListRow(
        key: const ValueKey('push-notifications-unsupported-platform'),
        icon: LucideIcons.bell,
        title: 'Push notifications',
        subtitle: 'Not yet supported on Android',
      ),
    ],
  );
}

Happy to open a PR if the copy is agreed.

Version and platform

• Buzz version: 0.5.23
• OS: Android
• Relay: hosted twelfth-ai.communities.buzz.xyz, relay software 0.2.1
• Verified at block/buzz@312cf67

Related: #6092, #7482