feat(client): 应用内更新（Windows/macOS 下载安装，Web 刷新）

- 新增 lib/core/update/：app_updater(入口+进度对话框) + io/web 条件实现
  - Windows: Dio 下载 setup.exe(无 MOTW) -> 启动安装包 -> 退出，规避浏览器
    SmartScreen 下载页与运行时拦截
  - macOS: 下载 zip -> ditto 解压 -> 后台脚本等退出后替换 /Applications 内
    app 并重启（权限失败回退访达高亮）
  - Web: 刷新页面；其它平台回退浏览器下载
- app_shell 更新 banner/强制更新弹窗、设置页「立即更新」改走应用内更新
- 设置页「检查更新」加反馈（正在检查/已是最新/发现新版本/失败）
- jiu-installer.iss 加 CloseApplications=yes 便于覆盖

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/lib/screens/settings/settings_screen.dart

@@ -12,6 +12,7 @@ import 'package:url_launcher/url_launcher.dart';
 import '../../core/auth/auth_state.dart';
 import '../../core/config/app_config.dart';
 import '../../core/config/app_info.dart';
+import '../../core/update/app_updater.dart';
 import '../../core/theme/app_theme.dart';
 import '../../models/number_rule.dart';
 import '../../models/user.dart';
@@ -729,7 +730,7 @@ class _SettingsScreenState extends ConsumerState<SettingsScreen> {
                   value: 'v${updateInfo.latestVersion}',
                   valueColor: AppTheme.success,
                   trailing: TextButton(
-                    onPressed: () => launchUpdateUrl(updateInfo.downloadUrls),
+                    onPressed: () => startInAppUpdate(context, updateInfo),
                     child: const Text('立即更新'),
                   ),
                 )
@@ -739,8 +740,24 @@ class _SettingsScreenState extends ConsumerState<SettingsScreen> {
                   value: updateInfo != null ? '已是最新' : '检查中…',
                   valueColor: AppTheme.textSecondary,
                   trailing: TextButton(
-                    onPressed: () =>
-                        ref.read(updateProvider.notifier).forceCheck(),
+                    onPressed: () async {
+                      final messenger = ScaffoldMessenger.of(context);
+                      messenger.showSnackBar(
+                          const SnackBar(content: Text('正在检查更新…')));
+                      await ref.read(updateProvider.notifier).forceCheck();
+                      if (!context.mounted) return;
+                      final r = ref.read(updateProvider).valueOrNull;
+                      messenger.hideCurrentSnackBar();
+                      final String msg;
+                      if (r == null) {
+                        msg = '检查更新失败，请检查网络';
+                      } else if (r.hasUpdate) {
+                        msg = '发现新版本 v${r.latestVersion}';
+                      } else {
+                        msg = '已是最新版本（v${r.latestVersion}）';
+                      }
+                      messenger.showSnackBar(SnackBar(content: Text(msg)));
+                    },
                     child: const Text('检查更新'),
                   ),
                 ),

client/lib/screens/shell/app_shell.dart

@@ -10,6 +10,7 @@ import '../../core/theme/app_theme.dart';
 import '../../providers/connectivity_provider.dart';
 import '../../providers/shop_provider.dart';
 import '../../providers/update_provider.dart';
+import '../../core/update/app_updater.dart';
 
 class AppShell extends ConsumerStatefulWidget {
   final Widget child;
@@ -56,7 +57,7 @@ class _AppShellState extends ConsumerState<AppShell> {
           ),
           actions: [
             ElevatedButton(
-              onPressed: () => launchUpdateUrl(info.downloadUrls),
+              onPressed: () => startInAppUpdate(context, info),
               child: const Text('立即更新'),
             ),
           ],
@@ -237,8 +238,8 @@ class _AppShellState extends ConsumerState<AppShell> {
                                 ),
                               ),
                               TextButton(
-                                onPressed: () => launchUpdateUrl(
-                                    updateInfo.downloadUrls),
+                                onPressed: () =>
+                                    startInAppUpdate(context, updateInfo),
                                 style: TextButton.styleFrom(
                                     foregroundColor:
                                         const Color(0xFFF57F17)),