test(i18n): cover the i18n facade, selector, manifest routing + locale (T-462)

Tests for the epic's new code so the 95% floor holds: ClideSettings.i18n
string/interpolated null-safe + localizedCommandTitle; settings-renderer
localization (section/field/help/select/file, project-scope tag, didUpdateWidget);
extension-activation rollback + settings-contribution unregister; the Dutch
gate check; RootShell applying app.locale on boot; and prompt/conversation
tool-body + file-ref coverage. Also harden the menu toggle re-tap (capture the
button point while stable, then tapAt) so it no longer throws getCenter under
the serial coverage load.

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

test/widgets/clide_settings_test.dart

@@ -1,3 +1,5 @@
+import 'package:clide/clide.dart' show IpcResponse;
+import 'package:clide/extension/extension.dart' show CommandContribution;
 import 'package:clide/widgets/widgets.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -40,4 +42,66 @@ void main() {
     expect(mono, 'FiraMono');
     expect(ui, 'Inter');
   });
+
+  testWidgets('i18n.string returns the placeholder without a kernel (T-462)', (tester) async {
+    late String s;
+    await tester.pumpWidget(
+      Builder(
+        builder: (context) {
+          s = ClideSettings.i18n.string(context, 'k', namespace: 'x', placeholder: 'Fallback');
+          return const SizedBox();
+        },
+      ),
+    );
+    expect(s, 'Fallback');
+  });
+
+  testWidgets('i18n.interpolated applies replacers to the placeholder without a kernel', (tester) async {
+    late String s;
+    await tester.pumpWidget(
+      Builder(
+        builder: (context) {
+          s = ClideSettings.i18n.interpolated(
+            context,
+            'k',
+            namespace: 'x',
+            placeholder: 'Hi {name}',
+            replacers: [I18nReplacer(from: '{name}', replace: 'Jeroen')],
+          );
+          return const SizedBox();
+        },
+      ),
+    );
+    expect(s, 'Hi Jeroen');
+  });
+
+  testWidgets('localizedCommandTitle resolves titleKey, else falls back to the title (T-462)', (tester) async {
+    final withKey = CommandContribution(
+      id: 'a',
+      command: 'a',
+      title: 'Eng A',
+      titleKey: 'cmd.a',
+      i18nNamespace: 'x',
+      run: (_) async => IpcResponse.ok(id: '', data: const {}),
+    );
+    final noKey = CommandContribution(
+      id: 'b',
+      command: 'b',
+      title: 'Eng B',
+      run: (_) async => IpcResponse.ok(id: '', data: const {}),
+    );
+    late String a;
+    late String b;
+    await tester.pumpWidget(
+      Builder(
+        builder: (context) {
+          a = localizedCommandTitle(context, withKey); // no kernel → placeholder (the title)
+          b = localizedCommandTitle(context, noKey);
+          return const SizedBox();
+        },
+      ),
+    );
+    expect(a, 'Eng A');
+    expect(b, 'Eng B');
+  });
 }