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/vim/src/vim_mode_indicator.dart

@@ -1,5 +1,4 @@
 import 'package:clide/builtin/vim/src/vim_mode_service.dart';
-import 'package:clide/kernel/kernel.dart';
 import 'package:clide/widgets/widgets.dart';
 import 'package:flutter/widgets.dart';
 
@@ -17,7 +16,7 @@ class VimModeIndicator extends StatelessWidget {
       listenable: service,
       builder: (context, _) {
         if (!service.enabled) return const SizedBox.shrink();
-        final tokens = ClideTheme.of(context).surface;
+        final tokens = ClideSettings.theme.of(context).surface;
         return Padding(
           padding: const EdgeInsets.symmetric(horizontal: 8),
           child: ClideText(