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_en.arb

@@ -149,6 +149,8 @@
   "accountSignOutTitle": "Sign out?",
   "accountDelete": "Delete account",
   "accountDeleteTitle": "Delete your account?",
+  "accountSignOutFailed": "Couldn't sign out on this device. Try again.",
+  "accountDeleteFailed": "Couldn't delete your account: the instance wasn't reached. Try again.",
   "aboutSourceCode": "The source of what this instance runs:",
   "aboutSourceUnreachable": "Couldn't reach this instance to ask where its source is.",
   "sessionUnreachable": "Couldn't reach the server.",