feat(purchase): 新增 Apple 内购完整链路

- AppleReceiptController 改造：验签后立刻落库并解锁权益
- 新增 ApplePurchaseService 处理业务：防重、写订单、发道具
- 新增 KeyboardUserPurchaseRecords 实体与 Mapper，记录用户购买
- ErrorCode 补充 RECEIPT_INVALID(50016)
- 删除过期 AGENTS.md，修正 i18n_message 表名与 CORS 白名单

src/main/java/com/yolo/keyborad/mapper/KeyboardUserPurchaseRecordsMapper.java

@@ -0,0 +1,12 @@
+package com.yolo.keyborad.mapper;
+
+import com.baomidou.mybatisplus.core.mapper.BaseMapper;
+import com.yolo.keyborad.model.entity.KeyboardUserPurchaseRecords;
+
+/*
+* @author: ziin
+* @date: 2025/12/12 15:16
+*/
+    
+public interface KeyboardUserPurchaseRecordsMapper extends BaseMapper<KeyboardUserPurchaseRecords> {
+}