fix(auth): only a session made since dismisses the owner's warning

The full reading's L1: the warning that ten wrong proofs ended a session is
there for the owner to learn of it, and any other session of the account
(another app on the same stolen phone) dismissed it. Now only a session
made after the warning dismisses it (signed in again, or the sign-in that
first shows it); an older one is refused (PasswordRefusal.signedInBefore,
its own text in English and German), and a new password clears it as
before. A member tells the register when its session asking was made.

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_en.dart

@@ -857,6 +857,10 @@ class HalkyonAppLocalizationsEn extends HalkyonAppLocalizations {
   String passwordSectionGitHubEndsDeletes(String date) {
     return 'Sign-in with GitHub ends on $date. Your account, with everything in it, will be deleted then, unless you set up a password before.';
   }
+
+  @override
+  String get passwordSignedInBefore =>
+      'Only a device signed in since then can dismiss this warning: sign in again on this one, or change your password.';
 }
 
 /// The translations for English, as used in the United Kingdom (`en_GB`).