feat(app): adding SimpleLogin to an account (ADR 0020, D21, D23)

halkyon_app reads where the device's person stands with SimpleLogin
(nothing to show, linked, or missing) and shows it in SimpleLoginSection,
which each app places above the password part: Add SimpleLogin, once
added one more way in. GitHub is added to nobody where SimpleLogin is
offered, and Learn's Profile offers an anonymous person SimpleLogin
alone there (D23).

No cut-off day, reminder or banner (D24): with the developer the only
person on learn.halkyon.eu, the cut-off is the operator taking GitHub's
OAuth app out of the deploy's settings once that account has SimpleLogin.
ADR 0020 records it and drops step 5.

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_de.dart

@@ -1051,4 +1051,17 @@ class HalkyonAppLocalizationsDe extends HalkyonAppLocalizations {
   @override
   String get simpleLoginTooManyHandleChecks =>
       'Es wurden zu viele Handles ausprobiert. Versuch es in einer Stunde noch einmal.';
+
+  @override
+  String get simpleLoginSectionTitle => 'SimpleLogin';
+
+  @override
+  String get simpleLoginSignsYouIn => 'Meldet dich an';
+
+  @override
+  String get simpleLoginAddHint =>
+      'Melde dich mit SimpleLogin an, oder mit deinem Proton-Konto.';
+
+  @override
+  String get simpleLoginAdded => 'SimpleLogin hinzugefügt.';
 }