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/lib/features/settings/presentation/widgets/settings_section_widgets.dart

@@ -3,8 +3,6 @@ import 'package:flutter/material.dart';
 import '../../../../l10n/app_localizations.dart';
 import '../../../../shared/theme/app_color_palette.dart';
 import '../../../../shared/theme/design_tokens.dart';
-import '../../../../shared/widgets/toast/toast.dart';
-import '../../../../shared/widgets/toast/toast_type.dart';
 
 class SectionLabel extends StatelessWidget {
   const SectionLabel({super.key, required this.text});
@@ -420,12 +418,20 @@ class CoinPackageCard extends StatelessWidget {
     required this.price,
     required this.amount,
     this.badge,
+    this.onPurchase,
+    this.isPurchasing = false,
+    this.isAvailable = true,
+    this.unavailableMessage,
   });
 
   final String title;
   final String price;
   final int amount;
   final String? badge;
+  final VoidCallback? onPurchase;
+  final bool isPurchasing;
+  final bool isAvailable;
+  final String? unavailableMessage;
 
   @override
   Widget build(BuildContext context) {
@@ -483,32 +489,43 @@ class CoinPackageCard extends StatelessWidget {
               ],
             ),
             const SizedBox(height: AppSpacing.lg),
-            Row(
-              children: [
-                Text(
-                  price,
-                  style: Theme.of(
-                    context,
-                  ).textTheme.headlineMedium?.copyWith(color: colors.primary),
+            if (!isAvailable && unavailableMessage != null)
+              Text(
+                unavailableMessage!,
+                style: Theme.of(context).textTheme.bodySmall?.copyWith(
+                  color: colors.error,
                 ),
-                const Spacer(),
-                FilledButton(
-                  onPressed: () {
-                    Toast.show(
+              )
+            else
+              Row(
+                children: [
+                  Text(
+                    price,
+                    style: Theme.of(
                       context,
-                      l10n.settingsPurchasePending,
-                      type: ToastType.info,
-                    );
-                  },
-                  style: FilledButton.styleFrom(
-                    shape: RoundedRectangleBorder(
-                      borderRadius: BorderRadius.circular(AppRadius.full),
-                    ),
+                    ).textTheme.headlineMedium?.copyWith(color: colors.primary),
                   ),
-                  child: Text(l10n.settingsPurchaseButton),
-                ),
-              ],
-            ),
+                  const Spacer(),
+                  FilledButton(
+                    onPressed: isPurchasing || !isAvailable ? null : onPurchase,
+                    style: FilledButton.styleFrom(
+                      shape: RoundedRectangleBorder(
+                        borderRadius: BorderRadius.circular(AppRadius.full),
+                      ),
+                    ),
+                    child: isPurchasing
+                        ? SizedBox(
+                            width: 20,
+                            height: 20,
+                            child: CircularProgressIndicator(
+                              strokeWidth: 2,
+                              color: colors.onPrimary,
+                            ),
+                          )
+                        : Text(l10n.settingsPurchaseButton),
+                  ),
+                ],
+              ),
           ],
         ),
       ),