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>

lib/builtin/claude/src/conversation_view.dart

@@ -24,6 +24,8 @@ import 'package:clide/builtin/claude/src/prompt_card.dart';
 import 'package:clide/builtin/claude/src/transcript_reader.dart';
 import 'package:clide/builtin/claude/src/workflow_run.dart';
 import 'package:clide/kernel/src/facade.dart';
+import 'package:clide/kernel/src/keymap/intents.dart';
+import 'package:clide/kernel/src/keymap/pane_key_nav.dart';
 import 'package:clide/kernel/src/syntax/language_map.dart';
 import 'package:clide/kernel/src/theme/controller.dart';
 import 'package:clide/kernel/src/theme/tokens.dart';
@@ -387,10 +389,48 @@ class _ConversationViewState extends State<ConversationView> {
         return list;
       },
     );
-    return ColoredBox(
+    final body = ColoredBox(
       color: tokens.panelBackground,
       child: widget.wrapInSelectionArea ? ClideSelectionArea(child: sized) : sized,
     );
+    // Vim nav scrolls the conversation while this region holds focus under the
+    // vim preset (T-406): j/k by a line, ctrl+d/u by half a viewport, gg/G to
+    // the ends — G also re-arms follow-tail so new output keeps it pinned.
+    return PaneKeyNav(onNav: _onNav, child: body);
+  }
+
+  /// One "line" of scroll for j/k — a few text rows' worth.
+  static const double _lineScroll = 48;
+
+  void _onNav(NavIntent intent, int count) {
+    if (!_scroll.hasClients) return;
+    final p = _scroll.position;
+    final half = p.viewportDimension / 2;
+    switch (intent) {
+      case NavDownIntent():
+        _scrollBy(_lineScroll * count);
+      case NavUpIntent():
+        _scrollBy(-_lineScroll * count);
+      case NavPageDownIntent():
+        _scrollBy(half);
+      case NavPageUpIntent():
+        _scrollBy(-half);
+      case NavTopIntent():
+        _scroll.jumpTo(0);
+        _atBottom = false;
+      case NavBottomIntent():
+        _scroll.jumpTo(p.maxScrollExtent);
+        _atBottom = true; // re-arm follow-tail (T-297)
+      case NavExpandOrRightIntent() || NavCollapseOrLeftIntent() || NavActivateIntent():
+        break; // a reader pane has no expand/activate semantics
+    }
+  }
+
+  void _scrollBy(double delta) {
+    final p = _scroll.position;
+    final target = (p.pixels + delta).clamp(0.0, p.maxScrollExtent);
+    _scroll.jumpTo(target);
+    _atBottom = (p.maxScrollExtent - target) <= _bottomEpsilon;
   }
 }