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/screens/settings_screen.dart

@@ -7,19 +7,22 @@ import '../../../../shared/widgets/app_modal_dialog.dart';
 import '../../../../shared/widgets/gua_icon.dart';
 import '../../data/models/profile_settings.dart';
 import '../../data/repositories/invite_repository.dart';
+import '../models/legal_document_type.dart';
+import '../utils/legal_document_assets.dart';
 import 'account_delete_screen.dart';
 import '../widgets/settings_section_widgets.dart';
 import 'coin_center_screen.dart';
 import 'feedback_screen.dart';
 import 'general_settings_screen.dart';
 import 'invite_screen.dart';
-import 'legal_center_screen.dart';
+import 'legal_document_screen.dart';
 import 'profile_edit_screen.dart';
 
 class SettingsScreen extends StatefulWidget {
   const SettingsScreen({
     super.key,
     required this.account,
+    required this.userId,
     required this.settings,
     required this.coinBalance,
     required this.inviteRepository,
@@ -30,9 +33,11 @@ class SettingsScreen extends StatefulWidget {
     required this.onLogout,
     required this.onDeleteAccount,
     required this.onSaveProfile,
+    required this.onBalanceChanged,
   });
 
   final String account;
+  final String userId;
   final ProfileSettingsV1 settings;
   final int coinBalance;
   final InviteRepository inviteRepository;
@@ -43,7 +48,8 @@ class SettingsScreen extends StatefulWidget {
   final Future<void> Function() onLogout;
   final Future<void> Function() onDeleteAccount;
   final Future<ProfileSettingsV1> Function(ProfileSettingsV1 updated)
-  onSaveProfile;
+      onSaveProfile;
+  final void Function(int newBalance) onBalanceChanged;
 
   @override
   State<SettingsScreen> createState() => _SettingsScreenState();
@@ -119,35 +125,17 @@ class _SettingsScreenState extends State<SettingsScreen> {
                 background: colors.surfaceContainerHighest,
                 onTap: _openInvite,
               ),
-              SettingsMenuTile(
-                icon: Icons.description_outlined,
-                title: l10n.settingsLegalCenterTitle,
-                tint: colors.secondary,
-                background: colors.surfaceContainerHighest,
-                showDivider: false,
-                onTap: _openLegalCenter,
-              ),
-            ],
-          ),
-          const SizedBox(height: AppSpacing.xl),
-          SettingsGroupCard(
-            children: [
               SettingsMenuTile(
                 icon: Icons.feedback_outlined,
                 title: l10n.settingsFeedbackTitle,
                 tint: colors.primary,
                 background: colors.surfaceContainerHighest,
-                showDivider: false,
                 onTap: () => Navigator.of(context).push<void>(
                   MaterialPageRoute<void>(
                     builder: (_) => FeedbackScreen(apiClient: widget.apiClient),
                   ),
                 ),
               ),
-            ],
-          ),
-          SettingsGroupCard(
-            children: [
               SettingsMenuTile(
                 icon: Icons.person_rounded,
                 title: l10n.settingsAccountAndDataTitle,
@@ -159,6 +147,33 @@ class _SettingsScreenState extends State<SettingsScreen> {
             ],
           ),
           const SizedBox(height: AppSpacing.xl),
+          SettingsGroupCard(
+            children: [
+              SettingsMenuTile(
+                icon: Icons.info_outline_rounded,
+                title: l10n.aboutUs,
+                tint: colors.secondary,
+                background: colors.surfaceContainerHighest,
+                onTap: () => _openLegalDocument(LegalDocumentType.aboutUs),
+              ),
+              SettingsMenuTile(
+                icon: Icons.security_rounded,
+                title: l10n.privacyPolicy,
+                tint: colors.secondary,
+                background: colors.surfaceContainerHighest,
+                onTap: () => _openLegalDocument(LegalDocumentType.privacyPolicy),
+              ),
+              SettingsMenuTile(
+                icon: Icons.description_outlined,
+                title: l10n.termsOfService,
+                tint: colors.secondary,
+                background: colors.surfaceContainerHighest,
+                showDivider: false,
+                onTap: () => _openLegalDocument(LegalDocumentType.termsOfService),
+              ),
+            ],
+          ),
+          const SizedBox(height: AppSpacing.xl),
           FilledButton(
             onPressed: _confirmLogout,
             style: FilledButton.styleFrom(
@@ -180,7 +195,11 @@ class _SettingsScreenState extends State<SettingsScreen> {
   Future<void> _openCoinCenter() async {
     await Navigator.of(context).push<void>(
       MaterialPageRoute<void>(
-        builder: (_) => CoinCenterScreen(balance: widget.coinBalance),
+        builder: (_) => CoinCenterScreen(
+          balance: widget.coinBalance,
+          userId: widget.userId,
+          onBalanceChanged: widget.onBalanceChanged,
+        ),
       ),
     );
   }
@@ -229,9 +248,16 @@ class _SettingsScreenState extends State<SettingsScreen> {
     });
   }
 
-  Future<void> _openLegalCenter() async {
-    await Navigator.of(context).push<void>(
-      MaterialPageRoute<void>(builder: (_) => const LegalCenterScreen()),
+  void _openLegalDocument(LegalDocumentType type) {
+    final l10n = AppLocalizations.of(context)!;
+    final locale = Localizations.localeOf(context);
+    Navigator.of(context).push<void>(
+      MaterialPageRoute<void>(
+        builder: (_) => LegalDocumentScreen(
+          title: legalDocumentTitle(l10n, type),
+          assetPath: legalDocumentAssetPath(locale, type),
+        ),
+      ),
     );
   }