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/lib/halkyon_ui.dart

@@ -22,6 +22,7 @@ export 'src/widget/confirm_dialog.dart';
 export 'src/widget/count_badge.dart';
 export 'src/widget/count_stepper.dart';
 export 'src/widget/empty_list_message.dart';
+export 'src/widget/explained_title.dart';
 export 'src/widget/field_label.dart';
 export 'src/widget/floating_navigation_bar.dart';
 export 'src/widget/folding_tabs.dart';

packages/halkyon_ui/lib/src/widget/explained_title.dart

@@ -0,0 +1,22 @@
+import 'package:halkyon_ui/src/widget/help_button.dart';
+import 'package:material_ui/material_ui.dart';
+
+/// A section's or a setting's [title] with its [HelpButton] right beside
+/// it, opening [help] under the title (decided 3 Nov 2026: what explains
+/// is one tap away). In [style] where given, the surrounding text's
+/// otherwise, as a [ListTile]'s title; a long title wraps, the question
+/// mark kept beside its end.
+class const ExplainedTitle(
+  final String title, {
+  required final String help,
+  final TextStyle? style,
+  super.key,
+}) extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) => Row(
+    children: [
+      Flexible(child: Text(title, style: style)),
+      HelpButton(help, title: title),
+    ],
+  );
+}