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,