fix(todo): what failed on the account sheet shows on it

The sheet holds snack bars of its own (`hasSnackBars`), so a failed
deletion, sign-out or reading of the account says so on it rather than
behind its barrier.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

apps/todo/halkyon_todo_flutter/lib/src/account/account_sheet.dart

@@ -20,6 +20,9 @@ class const _AccountSheet() extends StatelessWidget {
     final l10n = AppLocalizations.of(context);
     return SheetScaffold(
       title: l10n.accountTitle,
+      // What failed (signing out, deleting the account, reading it) shows
+      // on the sheet, not behind its barrier.
+      hasSnackBars: true,
       body: Column(
         mainAxisSize: MainAxisSize.min,
         crossAxisAlignment: CrossAxisAlignment.stretch,

apps/todo/halkyon_todo_flutter/test/app/todo_app_test.dart

@@ -195,6 +195,32 @@ void main() {
     expect(find.text('Sign in with GitHub'), findsOneWidget);
   });
 
+  testWidgets('a deletion the instance never got says so on the account '
+      'sheet, the person still signed in', (tester) async {
+    await start(tester, usedBefore: true);
+    await openAccount(tester);
+    gateway.deletionError = Exception('No connection');
+
+    await tester.tap(find.text('Delete account'));
+    await tester.pumpAndSettle();
+    await tester.tap(find.text('Delete account').last);
+    await tester.pumpAndSettle();
+
+    expect(
+      find.descendant(
+        of: find.byType(SheetScaffold),
+        matching: find.widgetWithText(
+          SnackBar,
+          "Couldn't delete your account: the instance wasn't reached. "
+          'Try again.',
+        ),
+      ),
+      findsOneWidget,
+      reason: 'on the sheet, not behind its barrier',
+    );
+    expect(gateway.status, isA<SignedIn>());
+  });
+
   testWidgets('About names the source of what the instance runs, which both '
       'licences ask to offer', (tester) async {
     await start(tester, usedBefore: true);