fix decision first-click + editor reveal via retained reader nav

Two reveal-on-open bugs:

Decisions opened only on the second click (T-196): the detail view
subscribed in didChangeDependencies, which runs after the tab is
revealed, so the broadcast 'selection' that triggered the reveal was
already gone. Hoist the back/forward history out of per-view State into
a retained per-reader ReaderNav (kernel ChangeNotifier in a
ReaderNavRegistry, D-81). The nav records selections, emits 'load' (the
single channel readers display from), and survives mount/unmount — the
reader grabs nav.current on mount, so the first selection lands. Both
the markdown and decisions readers move to this model; the per-view
ReaderHistoryMixin and the markdown post-frame forward hack are gone.

The editor pane never opened (T-197): EditorExtension contributed a
workspace tab but nothing activated it on editor.open. Add an activate()
that reveals the tab on editor.opened / editor.active-changed; the
view's hydrate() pulls the active buffer on mount.

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

lib/builtin/editor/src/extension.dart

@@ -1,3 +1,5 @@
+import 'dart:async';
+
 import 'package:clide/builtin/editor/src/editor_view.dart';
 import 'package:clide/extension/extension.dart';
 import 'package:clide/kernel/kernel.dart';
@@ -15,6 +17,25 @@ class EditorExtension extends ClideExtension {
   @override
   List<String> get dependsOn => const [];
 
+  StreamSubscription<DaemonEvent>? _sub;
+
+  /// Reveal the editor tab when a buffer opens or becomes active.
+  /// `editor.open` opens the buffer daemon-side and emits the event,
+  /// but nothing else brings the workspace tab to front — without this
+  /// the editor never appears over the Claude pane (T-197). The view's
+  /// `hydrate()` pulls the active buffer once it mounts.
+  @override
+  Future<void> activate(ClideExtensionContext ctx) async {
+    _sub = ctx.events.on<DaemonEvent>().listen((e) {
+      if (e.subsystem != 'editor') return;
+      if (e.kind != 'editor.opened' && e.kind != 'editor.active-changed') return;
+      ctx.panels.activateTab(Slots.workspace, 'editor.active');
+    });
+  }
+
+  @override
+  Future<void> deactivate() async => _sub?.cancel();
+
   @override
   List<ContributionPoint> get contributions => [
         TabContribution(