fix(flutter): 选集条箭头靠右排列

test/player/player_fullscreen_test.dart

@@ -286,6 +286,30 @@ void main() {
     expect(find.byKey(const Key('player-interaction-rail')), findsOneWidget);
   });
 
+  testWidgets('should_push_episodes_arrow_to_pill_right', (tester) async {
+    // 宽屏下文案不会撑满胶囊，才能验证箭头是否被推到最右侧。
+    await _pumpApp(tester, size: const Size(900, 844));
+    await _openSeriesPlayer(tester);
+
+    final pill = tester.getRect(find.byKey(const Key('player-episodes-pill')));
+    final label = tester.getRect(
+      find
+          .descendant(
+            of: find.byKey(const Key('player-episodes-pill')),
+            matching: find.byType(Text),
+          )
+          .first,
+    );
+    final arrow = tester.getRect(
+      find.descendant(
+        of: find.byKey(const Key('player-episodes-pill')),
+        matching: find.byIcon(Icons.keyboard_arrow_up_rounded),
+      ),
+    );
+    expect(pill.right - arrow.right, closeTo(14, 0.5));
+    expect(arrow.left - label.right, closeTo(8, 0.5));
+  });
+
   testWidgets('should_show_rail_counts_from_detail_and_follow_server_results', (
     tester,
   ) async {