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/widgets/src/quick_open_overlay.dart

@@ -150,7 +150,7 @@ class _QuickOpenOverlayState extends State<QuickOpenOverlay> {
   @override
   Widget build(BuildContext context) {
     final kernel = ClideKernel.of(context);
-    final tokens = ClideTheme.of(context).surface;
+    final tokens = ClideSettings.theme.of(context).surface;
     return ListenableBuilder(
       listenable: kernel.quickOpen,
       builder: (ctx, _) {
@@ -262,7 +262,7 @@ class _QuickOpenItemState extends State<_QuickOpenItem> {
 
   @override
   Widget build(BuildContext context) {
-    final tokens = ClideTheme.of(context).surface;
+    final tokens = ClideSettings.theme.of(context).surface;
     final selected = widget.highlighted;
     // Split the basename from its directory so the filename reads first.
     final slash = widget.path.lastIndexOf('/');