refactor(i18n): route consumer reads through ClideSettings.i18n (T-474)

Migrate widget i18n reads from ClideKernel.of(context).i18n to the unified
ClideSettings.i18n.of(context) facade (D-101), so settings/theme/fonts/i18n
share one widget-facing entry point. The facade delegates to the same I18n
service, so behaviour is unchanged. Infra plumbing (KernelServices /
ExtensionManager fields, the slot-host Listenable.merge) keeps its direct
kernel reference.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/builtin/extensions_ui/src/extensions_notice.dart

@@ -18,7 +18,7 @@ class ExtensionsNotice extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final tokens = ClideTheme.of(context).surface;
-    final i = ClideKernel.of(context).i18n;
+    final i = ClideSettings.i18n.of(context);
     return Column(
       crossAxisAlignment: CrossAxisAlignment.start,
       children: [

lib/builtin/settings_ui/src/settings_category_view.dart

@@ -69,7 +69,7 @@ class SettingsSearchResults extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final tokens = ClideTheme.of(context).surface;
-    final i = ClideKernel.of(context).i18n;
+    final i = ClideSettings.i18n.of(context);
     final store = ClideKernel.of(context).settings;
     final registry = ClideKernel.of(context).settingsRegistry;
     return ListenableBuilder(
@@ -501,7 +501,7 @@ class _ScopeTagState extends State<_ScopeTag> {
     super.dispose();
   }
 
-  String _ns(String key, String fallback) => ClideKernel.of(context).i18n.string(key, namespace: _settingsNs, placeholder: fallback);
+  String _ns(String key, String fallback) => ClideSettings.i18n.of(context).string(key, namespace: _settingsNs, placeholder: fallback);
 
   ({String glyph, Color color, String tip, String label}) _appearance(SettingsScope? layer) {
     final tokens = ClideTheme.of(context).surface;

lib/builtin/settings_ui/src/settings_modal.dart

@@ -49,7 +49,7 @@ class _SettingsModalState extends State<SettingsModal> {
 
   @override
   Widget build(BuildContext context) {
-    final i = ClideKernel.of(context).i18n;
+    final i = ClideSettings.i18n.of(context);
     final tokens = ClideTheme.of(context).surface;
     final title = i.string('modal.title', namespace: SettingsModal.ns, placeholder: 'Settings');
 
@@ -140,7 +140,7 @@ class _CloseButton extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final tokens = ClideTheme.of(context).surface;
-    final i = ClideKernel.of(context).i18n;
+    final i = ClideSettings.i18n.of(context);
     final label = i.string('modal.close', namespace: SettingsModal.ns, placeholder: 'Close');
     final hint = i.string('modal.close.hint', namespace: SettingsModal.ns, placeholder: 'Close settings');
     return Semantics(
@@ -178,7 +178,7 @@ class _CategoryRail extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final tokens = ClideTheme.of(context).surface;
-    final i = ClideKernel.of(context).i18n;
+    final i = ClideSettings.i18n.of(context);
     final registry = ClideKernel.of(context).settingsRegistry;
     final searching = query.trim().isNotEmpty;
     return ListenableBuilder(
@@ -312,7 +312,7 @@ class _EmptyState extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final tokens = ClideTheme.of(context).surface;
-    final i = ClideKernel.of(context).i18n;
+    final i = ClideSettings.i18n.of(context);
     return Center(
       child: Padding(
         padding: const EdgeInsets.all(24),

lib/builtin/theme_picker/src/appearance_control.dart

@@ -19,7 +19,7 @@ class AppearanceThemeControl extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final controller = ClideKernel.of(context).theme;
-    final i = ClideKernel.of(context).i18n;
+    final i = ClideSettings.i18n.of(context);
     return ListenableBuilder(
       listenable: controller,
       builder: (context, _) {

lib/builtin/theme_picker/src/settings_view.dart

@@ -45,9 +45,8 @@ class _SettingsViewState extends State<SettingsView> {
 
   @override
   Widget build(BuildContext context) {
-    final kernel = ClideKernel.of(context);
     final tokens = ClideTheme.of(context).surface;
-    final i = kernel.i18n;
+    final i = ClideSettings.i18n.of(context);
     final themes = baseThemes(widget.controller.available);
     final currentBase = baseThemeName(widget.controller.currentName);
     final title = i.string('modal.title', namespace: SettingsView.ns, placeholder: 'Settings');

lib/src/shell/slot_host.dart

@@ -368,5 +368,5 @@ String resolveTabTitle(BuildContext context, TabContribution t) {
   final key = t.titleKey;
   final ns = t.i18nNamespace;
   if (key == null || ns == null) return t.title;
-  return ClideKernel.of(context).i18n.string(key, namespace: ns, placeholder: t.title);
+  return ClideSettings.i18n.of(context).string(key, namespace: ns, placeholder: t.title);
 }