fix(auth): GitHub-only accounts go at GitHub's end; only the anonymous add an address

The full reading's M1 and L6: once GitHub IDs were forgotten at
GITHUB_SIGN_IN_ENDS, an account that had signed in with GitHub alone
counted as anonymous, so a stolen session and any mailbox gave it a first
password and authenticator; and such accounts, with no way in left, were
never pruned. Now:

- at the end, the daily run that forgets the GitHub IDs first deletes the
  accounts that sign in with GitHub alone (no address, so never a
  password), with everything they have, members told (deletePerson); the
  app tells them for the three months before that their account goes then
  unless they set up a password (passwordSectionGitHubEndsDeletes, en/de);
- password.set adds an address without GitHub only for someone anonymous
  where the session lives (anonymousHere, which a member tells the
  register, as it tells freshGitHubSignIn); anyone else is refused before
  any code is used.

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.dart

@@ -1494,6 +1494,12 @@ abstract class HalkyonAppLocalizations {
   /// In en, this message translates to:
   /// **'Your password and a code call off every reset waiting.'**
   String get passwordCallOffIntro;
+
+  /// No description provided for @passwordSectionGitHubEndsDeletes.
+  ///
+  /// In en, this message translates to:
+  /// **'Sign-in with GitHub ends on {date}. Your account, with everything in it, will be deleted then, unless you set up a password before.'**
+  String passwordSectionGitHubEndsDeletes(String date);
 }
 
 class _HalkyonAppLocalizationsDelegate