fix(app): a sign-out or deletion that failed says so, its tile showing it under way

The account's tiles show a spinner on Sign out or Delete account while it
runs, start neither again meanwhile, and say once, in a snack bar, why one
failed ("Couldn't delete your account: the instance wasn't reached. Try
again."; "Couldn't sign out on this device. Try again."), in English and
German. The session gate no longer builds the person's app anew for that:
only the tiles follow it.

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

packages/halkyon_app/lib/l10n/halkyon_app_localizations_de.dart

@@ -155,6 +155,14 @@ class HalkyonAppLocalizationsDe extends HalkyonAppLocalizations {
   @override
   String get accountDeleteTitle => 'Dein Konto löschen?';
 
+  @override
+  String get accountSignOutFailed =>
+      'Abmelden auf diesem Gerät hat nicht geklappt. Versuch es noch einmal.';
+
+  @override
+  String get accountDeleteFailed =>
+      'Dein Konto wurde nicht gelöscht: Die Instanz war nicht erreichbar. Versuch es noch einmal.';
+
   @override
   String get aboutSourceCode =>
       'Der Quellcode dessen, was diese Instanz ausführt:';