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/core/editor/rich_content_view_test.dart

@@ -74,4 +74,83 @@ void main() {
     expect(tapped, 1);
     expect(tester.testTextInput.hasAnyClients, isFalse);
   }, variant: TargetPlatformVariant.all());
+
+  group('asked to centre', () {
+    Map<String, Object?> block(
+      String type,
+      String text, [
+      Map<String, Object?> data = const {},
+    ]) => {
+      'type': type,
+      'data': {
+        ...data,
+        'delta': [
+          {'insert': text},
+        ],
+      },
+    };
+
+    Future<void> showCentred(
+      WidgetTester tester,
+      List<Map<String, Object?>> blocks,
+    ) async {
+      tester.view.physicalSize = const Size(400, 800);
+      tester.view.devicePixelRatio = 1;
+      addTearDown(tester.view.reset);
+      await tester.pumpWidget(
+        MaterialApp(
+          localizationsDelegates: AppLocalizations.localizationsDelegates,
+          home: Scaffold(
+            body: ListView(
+              children: [
+                RichContentView(
+                  content: RichContent({
+                    'document': {'type': 'page', 'children': blocks},
+                  }),
+                  textAlign: TextAlign.center,
+                ),
+              ],
+            ),
+          ),
+        ),
+      );
+      await tester.pump(const Duration(seconds: 1));
+    }
+
+    double centreOf(WidgetTester tester, String text) =>
+        tester.getCenter(find.text(text, findRichText: true)).dx;
+    double leftOf(WidgetTester tester, String text) =>
+        tester.getTopLeft(find.text(text, findRichText: true)).dx;
+
+    testWidgets('centres paragraphs and headings', (tester) async {
+      await showCentred(tester, [
+        block('heading', 'Greetings', {'level': 2}),
+        block('paragraph', 'hola'),
+      ]);
+
+      expect(centreOf(tester, 'Greetings'), moreOrLessEquals(200, epsilon: 1));
+      expect(centreOf(tester, 'hola'), moreOrLessEquals(200, epsilon: 1));
+    });
+
+    testWidgets('leaves a list at the start: centred, its markers would '
+        'drift apart', (tester) async {
+      await showCentred(tester, [
+        block('bulleted_list', 'hola'),
+        block('bulleted_list', 'buenos días'),
+      ]);
+
+      expect(leftOf(tester, 'hola'), lessThan(60));
+      expect(leftOf(tester, 'buenos días'), leftOf(tester, 'hola'));
+    });
+
+    testWidgets('keeps the alignment a paragraph was given in the editor', (
+      tester,
+    ) async {
+      await showCentred(tester, [
+        block('paragraph', 'hola', {'align': 'left'}),
+      ]);
+
+      expect(leftOf(tester, 'hola'), lessThan(40));
+    });
+  });
 }