feat(learn): a learning path's Scroll view, chosen in the study settings

A path shows either one step at a time (Steps) or on one page (Scroll,
as Tomorrow University's): the steps one below the other up to the first
question not answered right, answered in place with a lock below it, the
page running on once it is right, Finish at its end. A text step is done
once its end was on screen. The outline of the steps (done ticked, the
one in view marked, those beyond the question locked, a tap scrolling
there) is a column from expanded windows on, a drawer from the bar below.

The choice is the person's study option (`StudyOptions.pathView`,
settings schema 15), in Settings › Study and the session settings.

Whats-New: Learning paths can show on one scrolling page with an outline beside them: choose Scroll under Settings › Study.
Whats-New-De: Lernpfade lassen sich auf einer scrollbaren Seite mit Gliederung daneben zeigen: unter Einstellungen › Lernen „Scrollen“ wählen.

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/learn/halkyon_learn_flutter/test/feature/settings/model/person_settings_test.dart

@@ -127,6 +127,27 @@ void main() {
     );
   });
 
+  test("a path's view survives a round trip, in the 15th schema; a payload "
+      "from before, or a view this app doesn't know, has Steps", () {
+    const settings = PersonSettings(
+      study: StudyOptions(pathView: PathView.scroll),
+    );
+
+    expect(settingsSchemaVersion, greaterThanOrEqualTo(15));
+    expect(decodeSettingsPayload(encodeSettingsPayload(settings)), settings);
+    for (final study in [
+      <String, Object?>{},
+      {'pathView': 'carousel'},
+    ]) {
+      expect(
+        decodeSettingsPayload(
+          encodePayload(14, {'studyTags': {}, 'study': study}),
+        ).study.pathView,
+        PathView.steps,
+      );
+    }
+  });
+
   test('study options keep their numbers in range', () {
     final options = const StudyOptions().copyWith(
       cardsPerRound: 50,