fix(reward): 为 ExpiredRewardItem 添加 rightTypeName getter 别名

解决 profile_page.dart 编译错误：
- 添加 rightTypeName getter 作为 allocationTypeName 的别名
- 保持与 PendingRewardItem/SettleableRewardItem 的接口一致

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/mobile-app/lib/core/services/reward_service.dart

@@ -136,6 +136,9 @@ class ExpiredRewardItem {
 
   /// 获取权益类型的中文名称
   String get allocationTypeName => getAllocationTypeName(allocationType);
+
+  /// 获取权益类型的中文名称（别名，与 PendingRewardItem/SettleableRewardItem 保持一致）
+  String get rightTypeName => allocationTypeName;
 }
 
 /// 奖励汇总信息 (从 reward-service 获取)