feat(app,learn): the device's appearance and language, halkyon_app's, as Learn's Settings show them

The developer asked for Todo, Train and Meditate to offer Learn's
Appearance and Language (ADR 0014's amendment of 4 Nov 2026). Their
model, store, cubit and card move into halkyon_app: Appearance and Look
(a BCP 47 tag, null for the device's language), FileLookStore keeping it
in the app's support folder as JSON written by rename (per device, not
synced, read before the first frame), LookCubit for the apps to provide
above InstanceGate, and LookSettingsCard / DeviceLookCard with the texts
moved from Learn's arbs (look*, the same words). Each app passes the
languages it speaks, named in their own language.

Learn keeps its stored choice where it was, among its DeviceSettings,
and feeds the shared card from them: no migration, so nobody's language
or appearance moves, and nothing changes on its screen.

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

@@ -2015,4 +2015,22 @@ class HalkyonAppLocalizationsDe extends HalkyonAppLocalizations {
   @override
   String get speechNoRecognizer =>
       'Auf diesem Gerät ist keine Spracherkennung installiert. Installiere eine, etwa FUTO Voice Input oder Googles Sprachdienste, und versuche es dann noch einmal.';
+
+  @override
+  String get lookAppearance => 'Darstellung';
+
+  @override
+  String get lookAppearanceDevice => 'Gerätedesign';
+
+  @override
+  String get lookAppearanceLight => 'Hell';
+
+  @override
+  String get lookAppearanceDark => 'Dunkel';
+
+  @override
+  String get lookLanguage => 'Sprache';
+
+  @override
+  String get lookLanguageDevice => 'Gerätesprache';
 }