fix: improve transfer recognition and local data safety

frontend/lib/features/auth/pages/login_page.dart

@@ -3,8 +3,8 @@ import 'package:go_router/go_router.dart';
 import 'package:miaoji_zhang/shared/api/api_client.dart';
 import 'package:miaoji_zhang/shared/api/auth_api.dart';
 import 'package:miaoji_zhang/shared/api/config_api.dart';
+import 'package:miaoji_zhang/features/auth/local_data_recovery.dart';
 import 'package:miaoji_zhang/shared/services/current_ledger_store.dart';
-import 'package:miaoji_zhang/shared/services/guest_merge_service.dart';
 import 'package:miaoji_zhang/shared/services/local_database.dart';
 import 'package:miaoji_zhang/shared/services/session_store.dart';
 import 'package:miaoji_zhang/shared/services/push_service.dart';
@@ -59,36 +59,14 @@ class _LoginPageState extends State<LoginPage> {
         : null;
     setState(() => _loading = true);
     try {
-      final closureCancelled = await AuthApi.login(
-        _user.text.trim(),
-        _pass.text,
-      );
-      final profile = await AuthApi.me();
+      final result = await AuthApi.login(_user.text.trim(), _pass.text);
+      final profile = result.profile;
       await PushService.instance.refresh();
       await CurrentLedgerStore.instance.ensureLoaded(force: true);
       if (!mounted) return;
-      if (guestSnapshot?['hasData'] == true) {
-        final shouldMerge = await showJzConfirmSheet(
-          context,
-          title: '发现游客数据',
-          message: '是否将本机游客账单、分类和预算导入当前账号？数据会放入独立的“游客数据”账本，原游客数据仍保留在本机。',
-          confirmLabel: '导入数据',
-        );
-        if (shouldMerge) {
-          try {
-            final result = await GuestMergeService.merge(guestSnapshot!);
-            if (mounted) {
-              _showMessage('已导入 ${result.transactionCount} 笔游客账单');
-            }
-          } catch (error) {
-            if (mounted) {
-              _showMessage('游客数据暂未导入：${apiErrorMessage(error)}');
-            }
-          }
-        }
-      }
+      await offerLocalDataRecovery(context, guestSnapshot: guestSnapshot);
       if (!mounted) return;
-      if (closureCancelled) _showMessage('已取消账号注销，欢迎回来');
+      if (result.accountClosureCancelled) _showMessage('已取消账号注销，欢迎回来');
       final destination = !profile.onboardingDone
           ? '/onboarding'
           : profile.appMode == 'ai'