feat(client): 关于页页脚改为 App 备案号-2A（工信部 App 备案 2026-07-15 下号，原型同步）

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

client/lib/screens/about/about_screen.dart

@@ -70,7 +70,8 @@ class _AboutScreenState extends ConsumerState<AboutScreen> {
                       InkWell(
                         onTap: () =>
                             launchUrl(Uri.parse('https://beian.miit.gov.cn')),
-                        child: Text('京ICP备2026039814号',
+                        // App 备案号（-2A，与网站号 -1 区分）：工信部要求 App 显著位置标注
+                        child: Text('京ICP备2026039814号-2A',
                             style: TextStyle(
                                 fontSize: AppDims.fsXs, color: t.faint)),
                       ),
@@ -136,7 +137,7 @@ class _AboutScreenState extends ConsumerState<AboutScreen> {
                 InkWell(
                   onTap: () =>
                       launchUrl(Uri.parse('https://beian.miit.gov.cn')),
-                  child: Text('京ICP备2026039814号',
+                  child: Text('京ICP备2026039814号-2A',
                       style: TextStyle(fontSize: AppDims.fsXs, color: t.faint)),
                 ),
               ],