feat: 实现 iOS Apple Pay 内购支付功能

前端:
- 集成 in_app_purchase 插件，实现 IAP 支付流程
- 添加支付模块 (payments/) 处理产品获取、购买、验证
- 积分中心页面集成 Apple Pay 购买入口
- 设置页面重构: 关于/隐私/协议直接展示，删除 legal_center 子页面
- 修复欢迎引导页滚动检测阈值问题
- 修复解卦结果页 iOS 侧滑返回手势被阻止的问题
- 邀请码绑定按钮临时禁用（待后端实现）

后端:
- 新增 apple_iap_transactions 表记录交易
- 实现 Apple 服务器端验证 (App Store Server API)
- 支付成功后自动发放积分
- 支持 Sandbox/Production 环境切换
- 添加退款处理和交易状态机

协议:
- 更新积分流水协议，支持 purchase/refund 类型
- 新增 PAYMENT_* 错误码

apps/ios/EryaoProducts.storekit

@@ -0,0 +1,134 @@
+{
+  "identifier" : "EryaoProducts",
+  "nonRenewingSubscriptions" : [
+
+  ],
+  "products" : [
+    {
+      "displayPrice" : "0.99",
+      "familyShareable" : false,
+      "internalID" : "new_user_pack_001",
+      "introductoryOffer" : null,
+      "localizations" : [
+        {
+          "description" : "新用户专属优惠套餐",
+          "displayName" : "新手包",
+          "locale" : "zh_CN"
+        }
+      ],
+      "productID" : "com.meeyao.qianwen.new_user_pack",
+      "referenceName" : "新手包",
+      "type" : "Consumable"
+    },
+    {
+      "displayPrice" : "6.00",
+      "familyShareable" : false,
+      "internalID" : "basic_pack_001",
+      "introductoryOffer" : null,
+      "localizations" : [
+        {
+          "description" : "基础信用点套餐",
+          "displayName" : "基础包",
+          "locale" : "zh_CN"
+        }
+      ],
+      "productID" : "com.meeyao.qianwen.basic_pack",
+      "referenceName" : "基础包",
+      "type" : "Consumable"
+    },
+    {
+      "displayPrice" : "18.00",
+      "familyShareable" : false,
+      "internalID" : "popular_pack_001",
+      "introductoryOffer" : null,
+      "localizations" : [
+        {
+          "description" : "热门信用点套餐",
+          "displayName" : "热门包",
+          "locale" : "zh_CN"
+        }
+      ],
+      "productID" : "com.meeyao.qianwen.popular_pack",
+      "referenceName" : "热门包",
+      "type" : "Consumable"
+    },
+    {
+      "displayPrice" : "68.00",
+      "familyShareable" : false,
+      "internalID" : "premium_pack_001",
+      "introductoryOffer" : null,
+      "localizations" : [
+        {
+          "description" : "高级信用点套餐",
+          "displayName" : "高级包",
+          "locale" : "zh_CN"
+        }
+      ],
+      "productID" : "com.meeyao.qianwen.premium_pack",
+      "referenceName" : "高级包",
+      "type" : "Consumable"
+    }
+  ],
+  "settings" : {
+    "_applicationInternalID" : "6738123456",
+    "_developerTeamID" : "YOUR_TEAM_ID",
+    "_failTransactionsEnabled" : false,
+    "_lastSynchronizedDate" : 756460800,
+    "_locale" : "zh_CN",
+    "_storefront" : "CHN",
+    "_storeKitErrors" : [
+      {
+        "current" : null,
+        "enabled" : false,
+        "name" : "Load Products"
+      },
+      {
+        "current" : null,
+        "enabled" : false,
+        "name" : "Purchase"
+      },
+      {
+        "current" : null,
+        "enabled" : false,
+        "name" : "Verification"
+      },
+      {
+        "current" : null,
+        "enabled" : false,
+        "name" : "App Store Sync"
+      },
+      {
+        "current" : null,
+        "enabled" : false,
+        "name" : "Subscription Status"
+      },
+      {
+        "current" : null,
+        "enabled" : false,
+        "name" : "App Transaction"
+      },
+      {
+        "current" : null,
+        "enabled" : false,
+        "name" : "Manage Subscriptions Sheet"
+      },
+      {
+        "current" : null,
+        "enabled" : false,
+        "name" : "Refund Request Sheet"
+      },
+      {
+        "current" : null,
+        "enabled" : false,
+        "name" : "Offer Code Redeem Sheet"
+      }
+    ]
+  },
+  "subscriptionGroups" : [
+
+  ],
+  "version" : {
+    "major" : 4,
+    "minor" : 0
+  }
+}