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/clide_code_block.dart

@@ -1,7 +1,6 @@
 import 'dart:convert';
 
 import 'package:clide/kernel/src/syntax/tree_sitter_service.dart';
-import 'package:clide/kernel/src/theme/controller.dart';
 import 'package:clide/widgets/src/typography.dart';
 import 'package:flutter/widgets.dart';
 
@@ -51,7 +50,7 @@ class _ClideCodeBlockState extends State<ClideCodeBlock> {
 
   @override
   Widget build(BuildContext context) {
-    final tokens = ClideTheme.of(context).surface;
+    final tokens = ClideSettings.theme.of(context).surface;
     final style = TextStyle(
       fontFamily: ClideSettings.fonts.monoOf(context),
       fontFamilyFallback: clideMonoFamilyFallback,