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

backend/src/v1/points/router.py

@@ -44,6 +44,7 @@ async def get_available_packages(
         packages=[
             PackageInfo(
                 productCode=pkg.product_code,
+                appStoreProductId=pkg.app_store_product_id,
                 type=pkg.type.value,
                 price=pkg.price,
                 credits=pkg.credits,

backend/src/v1/points/schemas.py

@@ -19,6 +19,9 @@ class PackageInfo(BaseModel):
     model_config = ConfigDict(populate_by_name=True, serialize_by_alias=True)
 
     product_code: str = Field(alias="productCode", min_length=1, max_length=128)
+    app_store_product_id: str = Field(
+        alias="appStoreProductId", min_length=1, max_length=256
+    )
     type: Literal["starter", "regular"]
     price: float = Field(ge=0)
     credits: int = Field(ge=1)

backend/src/v1/points/service.py

@@ -23,6 +23,7 @@ from schemas.domain.points import (
 from schemas.enums import PointsBizType, PointsChangeType, PointsOperatorType
 from schemas.domain.points import ApplyPointsChangeCommand
 from schemas.shared.user import parse_profile_settings
+from v1.payments.service import _load_product_mappings
 from v1.points.repository import PointsRepository
 
 if TYPE_CHECKING:
@@ -67,6 +68,7 @@ class RegisterBonusResult:
 @dataclass(frozen=True)
 class PackageInfoResult:
     product_code: str
+    app_store_product_id: str
     type: PackageType
     price: float
     credits: int
@@ -461,6 +463,8 @@ class PointsService:
                 email_hash=email_hash
             )
 
+        product_mappings = _load_product_mappings()
+
         packages: list[PackageInfoResult] = []
         for pkg in pkg_config.packages:
             if not pkg.enabled:
@@ -468,9 +472,13 @@ class PointsService:
             if pkg.type == PackageType.STARTER and has_starter:
                 continue
 
+            mapping = product_mappings.get(pkg.product_code)
+            app_store_product_id = mapping.app_store_product_id if mapping else ""
+
             packages.append(
                 PackageInfoResult(
                     product_code=pkg.product_code,
+                    app_store_product_id=app_store_product_id,
                     type=pkg.type,
                     price=pkg.price,
                     credits=pkg.credits,