keyboard-operable ClideTappable + palette nav (T-100)

Plug widgets into the keymap layer landed in T-117.

ClideTappable:
  - Wrap in `Actions(ActivateIntent → onTap)` outside a `Focus` so
    dispatch from the focused context walks up and hits the action.
  - Add a focus ring via `tokens.globalFocus` (DecoratedBox foreground
    overlay, transparent border when unfocused, no layout shift).
  - Disabled (`onTap == null`) skips focus traversal and shows the
    forbidden cursor.

ClidePalette:
  - Register Actions for the four palette intents
    (selectNext / selectPrev / accept / dismiss).
  - Publish `palette.open` scope flag via `KeymapService.setScopeFlag`
    so when-clauses can scope future bindings to "palette only".
  - Highlight the selected row with `listItemSelectedBackground`;
    scroll it into view on nav.
  - `PaletteController` grows `selectedIndex` + `selectNext` /
    `selectPrevious` / `acceptSelected`; index resets on open /
    filter change.

Intents.dart drops the `ClideIntent` base — `ActivateIntent` and
`DismissIntent` come from Flutter; clide owns the palette and text-
scale and command-bridge subclasses. `parseIntentId('activate')` →
Flutter's class; same for dismiss. Widget code uses the canonical
Flutter Intent types where they fit.

App root grows a PaletteOpenIntent action that calls
`services.palette.open()`, completing the ctrl/cmd+shift+p path
end-to-end.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lib/kernel/src/commands/palette.dart

@@ -9,13 +9,26 @@ class PaletteController extends ChangeNotifier {
 
   bool _open = false;
   String _filter = '';
+  int _selectedIndex = 0;
 
   bool get isOpen => _open;
   String get filter => _filter;
 
+  /// Index of the highlighted entry inside the currently-filtered
+  /// list. Clamped to `[0, filtered().length - 1]` on read. Returns 0
+  /// when the filter excludes everything.
+  int get selectedIndex {
+    final n = filtered().length;
+    if (n == 0) return 0;
+    if (_selectedIndex < 0) return 0;
+    if (_selectedIndex >= n) return n - 1;
+    return _selectedIndex;
+  }
+
   void open() {
     if (_open) return;
     _open = true;
+    _selectedIndex = 0;
     notifyListeners();
   }
 
@@ -23,6 +36,7 @@ class PaletteController extends ChangeNotifier {
     if (!_open) return;
     _open = false;
     _filter = '';
+    _selectedIndex = 0;
     notifyListeners();
   }
 
@@ -31,9 +45,35 @@ class PaletteController extends ChangeNotifier {
   void setFilter(String f) {
     if (_filter == f) return;
     _filter = f;
+    _selectedIndex = 0;
     notifyListeners();
   }
 
+  /// Highlight the next entry, wrapping at the end. No-op when the
+  /// filtered list has fewer than 2 entries.
+  void selectNext() {
+    final n = filtered().length;
+    if (n < 2) return;
+    _selectedIndex = (selectedIndex + 1) % n;
+    notifyListeners();
+  }
+
+  /// Highlight the previous entry, wrapping at the start.
+  void selectPrevious() {
+    final n = filtered().length;
+    if (n < 2) return;
+    _selectedIndex = (selectedIndex - 1 + n) % n;
+    notifyListeners();
+  }
+
+  /// Invoke whatever's currently highlighted; no-op when the filter
+  /// excludes everything.
+  Future<void> acceptSelected() async {
+    final list = filtered();
+    if (list.isEmpty) return;
+    await invoke(list[selectedIndex].command);
+  }
+
   List<CommandContribution> filtered() {
     if (_filter.isEmpty) return _registry.all.toList();
     final q = _filter.toLowerCase();