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_de.arb

@@ -39,6 +39,8 @@
   "accountSignOutTitle": "Abmelden?",
   "accountDelete": "Konto löschen",
   "accountDeleteTitle": "Dein Konto löschen?",
+  "accountSignOutFailed": "Abmelden auf diesem Gerät hat nicht geklappt. Versuch es noch einmal.",
+  "accountDeleteFailed": "Dein Konto wurde nicht gelöscht: Die Instanz war nicht erreichbar. Versuch es noch einmal.",
   "aboutSourceCode": "Der Quellcode dessen, was diese Instanz ausführt:",
   "aboutSourceUnreachable": "Diese Instanz war nicht erreichbar, um nach ihrem Quellcode zu fragen.",
   "sessionUnreachable": "Der Server war nicht erreichbar.",