refactor(theme): route consumer reads through ClideSettings.theme (T-473)

Migrate ClideTheme.of(context) reads across the widget, feature, and shell
layers to the unified ClideSettings.theme.of(context) facade (D-101), so
theme/i18n/fonts/settings share one widget-facing entry. The facade delegates
straight to ClideTheme, so behaviour is unchanged — goldens are unmoved.

The low-level theme provider keeps its direct ClideTheme.of: the facade is
built on it, and the two kernel sites (ClideTheme's own definition + the
panels drag-resize widget) stay direct to avoid a widgets→kernel import cycle.
Dead controller.dart/kernel.dart imports left by the sweep removed.

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

lib/builtin/git/src/git_status_item.dart

@@ -56,7 +56,7 @@ class _GitStatusItemState extends State<GitStatusItem> {
 
   @override
   Widget build(BuildContext context) {
-    final tokens = ClideTheme.of(context).surface;
+    final tokens = ClideSettings.theme.of(context).surface;
     if (_branch == null) return const SizedBox.shrink();
     final parts = <String>[_branch!];
     if (_ahead > 0) parts.add('↑$_ahead');
@@ -143,7 +143,7 @@ class _BranchPickerState extends State<_BranchPicker> {
 
   @override
   Widget build(BuildContext context) {
-    final tokens = ClideTheme.of(context).surface;
+    final tokens = ClideSettings.theme.of(context).surface;
     return Focus(
       focusNode: _focus,
       onKeyEvent: _onKey,
@@ -215,7 +215,7 @@ class _BranchRow extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final tokens = ClideTheme.of(context).surface;
+    final tokens = ClideSettings.theme.of(context).surface;
     return ClideTappable(
       onTap: onTap,
       cursor: onTap != null ? SystemMouseCursors.click : MouseCursor.defer,