fix(auth)!: a first password takes a fresh proof of the account's way in

The fourth reading's first finding: password.set took a session alone,
so whoever took one made a GitHub-only account, or an address account
without a password, theirs for good (their address or password, their
authenticator; GitHub then refused the owner).

- An account with an address proves it anew: a code mailed to that
  address for this (EmailCodePurpose.firstPassword, its own mail), never
  the session alone, a code asked for anything else, or another address.
- An account that signs in with GitHub alone does it within 10 minutes of
  a GitHub sign-in (the session's method and creation time, where the
  session lives; members tell the register), refused signInAgain before
  any code is used; the address it adds is proved as before.
- Anonymous people still become identified with a code to the address
  they add.

The app mails the code to the person's own address (asking for it where
the device doesn't know it), offers a password right after a GitHub
sign-in (D2's "at their next sign-in") before the person's app, and asks
for a GitHub sign-in anew when the instance refuses an older one, keeping
the code typed.

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

@@ -794,6 +794,23 @@ class HalkyonAppLocalizationsEn extends HalkyonAppLocalizations {
   @override
   String get passwordChangedSignInAgain =>
       'Your password was changed, but this service couldn\'t sign you in just yet. Sign in again with the new password.';
+
+  @override
+  String get passwordSignInAgain =>
+      'To give an account that signs in with GitHub its password, sign in with GitHub again first: it has been more than a few minutes.';
+
+  @override
+  String get passwordSignInWithGitHubAgain => 'Sign in with GitHub again';
+
+  @override
+  String get passwordOfferTitle => 'Set up a password';
+
+  @override
+  String get passwordOfferBody =>
+      'Sign-in with GitHub is ending. Set up a password and an authenticator app to keep your account.';
+
+  @override
+  String get passwordOfferLater => 'Later';
 }
 
 /// The translations for English, as used in the United Kingdom (`en_GB`).