feat(i18n): i18n key fields on command + settings contributions (T-462)

Lets manifest labels (command-palette/menu titles, settings labels) localize,
not just displayed widget strings. Adds optional titleKey/i18nNamespace to
CommandContribution and labelKey/helpKey/titleKey + a category i18nNamespace to
the settings schema. The command palette and menu bar now resolve titles via a
shared localizedCommandTitle helper — and the palette's fuzzy search matches
the localized title too (PaletteController.titleResolver). No behaviour change
until the per-extension keys + catalog entries land (placeholder == English).

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

lib/builtin/menubar/src/menu_bar.dart

@@ -72,7 +72,13 @@ class MenuBar extends StatelessWidget {
     return ListenableBuilder(
       listenable: Listenable.merge([controller, kernel.commands, kernel.project]),
       builder: (ctx, _) {
-        final menus = resolveMenus(buildClideMenuTree(), kernel.commands, kernel, bindingLabel: (id) => keymapBindingLabel(kernel.keymap, id));
+        final menus = resolveMenus(
+          buildClideMenuTree(),
+          kernel.commands,
+          kernel,
+          bindingLabel: (id) => keymapBindingLabel(kernel.keymap, id),
+          localizeTitle: (c) => localizedCommandTitle(context, c),
+        );
         controller.setMnemonics([for (final m in menus) m.title[m.mnemonic].toLowerCase()]);
         return Row(
           mainAxisSize: MainAxisSize.min,

lib/builtin/menubar/src/menu_model.dart

@@ -108,7 +108,13 @@ String? keymapBindingLabel(KeymapService keymap, String commandId) {
 /// menus. [bindingLabel] supplies the keybinding string for a command id
 /// (typically [keymapBindingLabel] bound to the keymap); when it returns null
 /// the command's own `defaultBinding` is used as a fallback.
-List<ResolvedMenu> resolveMenus(List<TopMenu> tree, CommandRegistry registry, KernelServices services, {String? Function(String commandId)? bindingLabel}) {
+List<ResolvedMenu> resolveMenus(
+  List<TopMenu> tree,
+  CommandRegistry registry,
+  KernelServices services, {
+  String? Function(String commandId)? bindingLabel,
+  String Function(CommandContribution cmd)? localizeTitle,
+}) {
   final placed = <String>{
     for (final m in tree)
       for (final n in m.nodes)
@@ -130,7 +136,7 @@ List<ResolvedMenu> resolveMenus(List<TopMenu> tree, CommandRegistry registry, Ke
   ResolvedItem resolveItem(MenuCommandItem item) {
     final cmd = registry.get(item.commandId);
     final enabled = cmd != null && (item.enabledWhen?.call(services) ?? true);
-    final raw = cmd?.title ?? item.fallbackTitle ?? item.commandId;
+    final raw = (cmd != null ? (localizeTitle?.call(cmd) ?? cmd.title) : null) ?? item.fallbackTitle ?? item.commandId;
     return ResolvedItem(commandId: item.commandId, title: _stripCategory(raw), enabled: enabled, keybinding: label(item.commandId));
   }