feat(learn,app): explanations wait behind a question mark beside their title

What explains a setting or a section, rather than what is the person's
own, moves behind halkyon_ui's HelpButton, beside its title through the
new ExplainedTitle (the developer's review of 3 Nov 2026): in Learn's
settings (citations, the Pomodoro timer, grammar, the web search,
Jellyfin, the device's dictionaries, counting one's learning), the study
settings, export's progress, the Jellyfin tags and the study button's
back first; in halkyon_app, setting up a password, adding SimpleLogin,
own keys not allowed, the profile page's link back and the operator's
grant sheet.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

packages/halkyon_ui/test/widget/explained_title_test.dart

@@ -0,0 +1,52 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:halkyon_ui/halkyon_ui.dart';
+import 'package:material_ui/material_ui.dart';
+
+import '../support/test_app.dart';
+
+void main() {
+  testWidgets('a title with its question mark right beside it, the '
+      'explanation opening under the title', (tester) async {
+    await tester.pumpWidget(
+      testApp(
+        const Scaffold(
+          body: SizedBox(
+            width: 300,
+            child: ListTile(
+              title: ExplainedTitle(
+                'Check spelling',
+                help: 'Underlines possible mistakes.',
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+    expect(find.text('Underlines possible mistakes.'), findsNothing);
+    final title = tester.getRect(find.text('Check spelling'));
+    final help = tester.getRect(find.byType(HelpButton));
+    expect(help.left - title.right, lessThan(8), reason: 'beside it');
+
+    await tester.tap(find.byType(HelpButton));
+    await tester.pumpAndSettle();
+    expect(find.text('Check spelling'), findsNWidgets(2));
+    expect(find.text('Underlines possible mistakes.'), findsOneWidget);
+  });
+
+  testWidgets('a long title wraps, its question mark kept', (
+    tester,
+  ) async {
+    await tester.pumpWidget(
+      testApp(
+        Scaffold(
+          body: SizedBox(
+            width: 200,
+            child: ExplainedTitle('A title ' * 20, help: 'Why.'),
+          ),
+        ),
+      ),
+    );
+    expect(tester.takeException(), isNull);
+    expect(find.byType(HelpButton), findsOneWidget);
+  });
+}