lift text-zoom into kernel, surface it in the palette (T-114)

Workspace text-zoom (Ctrl +/-/0) was local state on _RootShellState,
reachable only via the keymap intent path. Lifted to a kernel TextZoom
ChangeNotifier so the new `view.zoomIn/Out/Reset` palette commands
mutate the same number the keymap does — closing T-114's "discoverable
in the palette" item.

Co-Authored-By: Claude <noreply@anthropic.com>

lib/kernel/src/facade.dart

@@ -5,6 +5,7 @@ import 'package:clide/clide.dart';
 import 'package:clide/kernel/src/clipboard.dart';
 import 'package:clide/kernel/src/commands/keybindings.dart';
 import 'package:clide/kernel/src/keymap/keymap_service.dart';
+import 'package:clide/kernel/src/text_zoom.dart';
 import 'package:clide/kernel/src/commands/palette.dart';
 import 'package:clide/kernel/src/commands/registry.dart';
 import 'package:clide/kernel/src/dialog.dart';
@@ -65,6 +66,7 @@ class KernelServices {
     required this.toolchain,
     required this.scheduler,
     required this.keymap,
+    required this.textZoom,
   });
 
   final Logger log;
@@ -94,6 +96,7 @@ class KernelServices {
   final Toolchain toolchain;
   final SchedulerService scheduler;
   final KeymapService keymap;
+  final TextZoom textZoom;
 
   static Future<KernelServices> boot({
     required Directory appDir,
@@ -151,6 +154,7 @@ class KernelServices {
     final tc = toolchain ?? Toolchain();
     final scheduler = SchedulerService(events);
     scheduler.start();
+    final textZoom = TextZoom();
     final project = ProjectManager(
       log: log,
       events: events,
@@ -225,6 +229,7 @@ class KernelServices {
       toolchain: tc,
       scheduler: scheduler,
       keymap: keymap,
+      textZoom: textZoom,
     );
   }
 
@@ -247,6 +252,7 @@ class KernelServices {
     extensions.dispose();
     await scheduler.dispose();
     keymap.dispose();
+    textZoom.dispose();
     await log.dispose();
     messages.dispose();
     await events.dispose();

lib/kernel/src/text_zoom.dart

@@ -0,0 +1,28 @@
+import 'package:flutter/foundation.dart';
+
+/// Workspace-wide text zoom factor.
+///
+/// Owned by the kernel rather than the root widget so command-palette
+/// entries, the keymap layer, and any future menu/CLI surface can mutate
+/// the same number. The root `MediaQuery` listens via [ChangeNotifier].
+class TextZoom extends ChangeNotifier {
+  TextZoom();
+
+  static const double minScale = 0.6;
+  static const double maxScale = 2.0;
+  static const double stepScale = 0.05;
+
+  double _scale = 1.0;
+  double get scale => _scale;
+
+  void increase() => _setScale(_scale + stepScale);
+  void decrease() => _setScale(_scale - stepScale);
+  void reset() => _setScale(1.0);
+
+  void _setScale(double next) {
+    final clamped = next.clamp(minScale, maxScale);
+    if (clamped == _scale) return;
+    _scale = clamped;
+    notifyListeners();
+  }
+}