refactor(todo,meditate,train): a title with its question mark is halkyon_ui's ExplainedTitle

Three forks of the 3 Nov review each wrote the same widget (Todo's and
Meditate's TitleWithHelp, Train's HelpTitle); halkyon_ui's ExplainedTitle,
from Learn's, takes their place.

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

apps/train/halkyon_train_flutter/test/core/widget/explained_title_test.dart

@@ -0,0 +1,44 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:halkyon_ui/halkyon_ui.dart';
+import 'package:material_ui/material_ui.dart';
+
+void main() {
+  testWidgets("a setting's title keeps its explanation behind the question "
+      'mark, and a tap on the title still reaches the tile', (tester) async {
+    var on = false;
+    await tester.pumpWidget(
+      MaterialApp(
+        localizationsDelegates: HalkyonUiLocalizations.localizationsDelegates,
+        home: Scaffold(
+          body: StatefulBuilder(
+            builder: (context, setState) => SwitchListTile(
+              title: const ExplainedTitle(
+                'Smaller copies',
+                help: 'Lossless files kept as Opus.',
+              ),
+              value: on,
+              onChanged: (value) => setState(() => on = value),
+            ),
+          ),
+        ),
+      ),
+    );
+    expect(find.text('Lossless files kept as Opus.'), findsNothing);
+
+    await tester.tap(find.text('Smaller copies'));
+    await tester.pump();
+    expect(on, isTrue);
+
+    await tester.tap(find.byType(HelpButton));
+    await tester.pumpAndSettle();
+    expect(find.text('Lossless files kept as Opus.'), findsOneWidget);
+    expect(
+      find.descendant(
+        of: find.byType(AlertDialog),
+        matching: find.text('Smaller copies'),
+      ),
+      findsOneWidget,
+    );
+    expect(on, isTrue, reason: 'the question mark leaves the switch alone');
+  });
+}