fix(app): study faces centred in the card

The read-only view passed its alignment to the text alone, which the
editor lays out only as wide as itself, so a centred face stayed at the
start. It now aligns top-level paragraphs and headings that have no
alignment of their own; lists, quotes and the rest keep the start, and
an alignment chosen in the format bar wins.

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

halkyon_learn_flutter/test/feature/study/widget/study_screen_test.dart

@@ -138,6 +138,28 @@ void main() {
     expect(find.textContaining('cat', findRichText: true), findsNothing);
   });
 
+  testWidgets('the faces are centred in the card, and a tap on their text '
+      'shows and hides the answer too', (tester) async {
+    await cards.create(
+      'japanese',
+      CardContent(front: paragraph('猫'), back: paragraph('cat')),
+    );
+    await study(tester, width: 400);
+    final card = tester.getRect(find.byType(StudyCardSurface));
+    double centreOf(String text) =>
+        tester.getCenter(find.text(text, findRichText: true)).dx;
+
+    expect(centreOf('猫'), moreOrLessEquals(card.center.dx, epsilon: 1));
+
+    await tester.tap(find.text('猫', findRichText: true));
+    await tester.pumpAndSettle();
+    expect(centreOf('cat'), moreOrLessEquals(card.center.dx, epsilon: 1));
+
+    await tester.tap(find.text('cat', findRichText: true));
+    await tester.pumpAndSettle();
+    expect(find.textContaining('cat', findRichText: true), findsNothing);
+  });
+
   testWidgets('on a phone, a card swiped right is rated Good, one let go '
       'early springs back', (tester) async {
     await cards.create(