vim normal-mode navigation in non-editor panes (T-406)

The structural T-403 child: make vim normal mode mean navigation in panes
that were mouse-only. The passive global key path can't run multi-chord
sequences (D-82), so each pane hosts its own SequenceMatcher — factored into
a reusable PaneKeyNav that resolves the live keymap and dispatches nav.*
intents while a pane holds focus under the vim preset.

- nav.* intents (down/up/pageDown/pageUp/top/bottom/expandOrRight/
  collapseOrLeft/activate) — preset-neutral; vim.yaml binds j/k/ctrl+d/ctrl+u/
  gg/G/l/h/[o,enter] under `vim.normal && !editor.focused`.
- The editor publishes an `editor.focused` scope flag from its focus node, so
  the same keys stay buffer motions while the editor is focused and become nav
  when a pane is — resolved by file order + the guard (no change to the editor
  motion bindings).
- File tree: a flattened visible-index selection cursor in FileTreeController
  (j/k move, h collapse-or-out, l expand-or-into, o/enter open), with a focus
  ring + scroll-into-view.
- Conversation: j/k line-scroll, ctrl+d/u half-page, gg top, G bottom — G
  re-arms follow-tail.

Foundation for T-404/T-405/T-407, which build on the per-pane matcher and the
editor.focused guard. Git panel + ticket board list nav deferred to a
follow-up (the ticket says lists can trail). Tests: keymap resolution under
both scopes, PaneKeyNav dispatch, the controller selection model, and
end-to-end key-driven nav in both panes.

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

test/builtin/claude/conversation_view_test.dart

@@ -14,10 +14,11 @@ import 'package:clide/builtin/claude/src/image_thumbnail.dart';
 import 'package:clide/builtin/claude/src/transcript_publisher.dart';
 import 'package:clide/builtin/claude/src/transcript_reader.dart';
 import 'package:clide/builtin/claude/src/workflow_run.dart';
+import 'package:clide/kernel/kernel.dart' show PaneKeyNav;
 import 'package:clide/kernel/src/events/message_bus.dart';
 import 'package:clide/widgets/widgets.dart';
 import 'package:flutter/services.dart';
-import 'package:flutter/widgets.dart' show Builder, Image, FileImage, MediaQuery, ValueKey;
+import 'package:flutter/widgets.dart' show Builder, Focus, Image, FileImage, MediaQuery, Scrollable, ScrollableState, ValueKey;
 import 'package:flutter_test/flutter_test.dart';
 
 import '../../helpers/kernel_fixture.dart';
@@ -199,6 +200,61 @@ void main() {
       expect(find.text('Waiting for Claude…'), findsOneWidget);
     });
 
+    testWidgets('vim G / gg / j scroll the conversation under vim.normal (T-406)', (tester) async {
+      await tester.runAsync(() => f.services.keymap.setPreset('vim'));
+      f.services.keymap.setScopeFlag('vim.normal', true);
+      addTearDown(() => f.services.keymap.clearScopeFlag('vim.normal'));
+
+      // Enough prose to overflow the 700px viewport so there's room to scroll.
+      await pumpWith(tester, [for (var i = 0; i < 40; i++) AssistantTextMessage(uuid: 'a$i', timestamp: _t, isSidechain: false, text: 'line number $i')]);
+
+      // Focus the pane's nav region (its own Focus is PaneKeyNav's outermost).
+      final node = tester.widget<Focus>(find.descendant(of: find.byType(PaneKeyNav), matching: find.byType(Focus)).first).focusNode!;
+      node.requestFocus();
+      await tester.pump();
+
+      final pos = tester.state<ScrollableState>(find.byType(Scrollable).first).position;
+      expect(pos.maxScrollExtent, greaterThan(0), reason: 'content must overflow to scroll');
+
+      // G → jump to the bottom.
+      await tester.sendKeyDownEvent(LogicalKeyboardKey.shiftLeft);
+      await tester.sendKeyEvent(LogicalKeyboardKey.keyG);
+      await tester.sendKeyUpEvent(LogicalKeyboardKey.shiftLeft);
+      await tester.pump();
+      expect(pos.pixels, pos.maxScrollExtent);
+
+      // gg → jump to the top.
+      await tester.sendKeyEvent(LogicalKeyboardKey.keyG);
+      await tester.sendKeyEvent(LogicalKeyboardKey.keyG);
+      await tester.pump();
+      expect(pos.pixels, 0);
+
+      // j → down one line (48px); k → back up.
+      await tester.sendKeyEvent(LogicalKeyboardKey.keyJ);
+      await tester.pump();
+      expect(pos.pixels, 48);
+      await tester.sendKeyEvent(LogicalKeyboardKey.keyK);
+      await tester.pump();
+      expect(pos.pixels, 0);
+
+      // ctrl+d / ctrl+u → half a viewport down then back up.
+      await tester.sendKeyDownEvent(LogicalKeyboardKey.controlLeft);
+      await tester.sendKeyEvent(LogicalKeyboardKey.keyD);
+      await tester.pump();
+      expect(pos.pixels, greaterThan(0));
+      await tester.sendKeyEvent(LogicalKeyboardKey.keyU);
+      await tester.sendKeyUpEvent(LogicalKeyboardKey.controlLeft);
+      await tester.pump();
+      expect(pos.pixels, 0);
+
+      // h / l / o have no reader-pane semantics — they don't move the scroll.
+      await tester.sendKeyEvent(LogicalKeyboardKey.keyL);
+      await tester.sendKeyEvent(LogicalKeyboardKey.keyH);
+      await tester.sendKeyEvent(LogicalKeyboardKey.keyO);
+      await tester.pump();
+      expect(pos.pixels, 0);
+    });
+
     testWidgets('a Workflow tool-use with a live run renders the workflow card (T-416)', (tester) async {
       var run = const WorkflowRun(toolUseId: 'x1', name: 'parallel-words');
       run = run.foldEvent({