fix(security): 修复修改登录密码页面加载失败时静默降级的 bug

与 change_payment_password_page 同款问题：加载失败时原本默默设为
hasPassword=true（注册时必须设置的假设），改为显示错误状态+重试按钮。

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/mobile-app/lib/features/security/presentation/pages/change_password_page.dart

@@ -40,6 +40,9 @@ class _ChangePasswordPageState extends ConsumerState<ChangePasswordPage> {
   /// 是否正在加载
   bool _isLoading = true;
 
+  /// 加载状态是否出错
+  bool _isLoadError = false;
+
   @override
   void initState() {
     super.initState();
@@ -58,6 +61,7 @@ class _ChangePasswordPageState extends ConsumerState<ChangePasswordPage> {
   Future<void> _loadPasswordStatus() async {
     setState(() {
       _isLoading = true;
+      _isLoadError = false;
     });
 
     try {
@@ -73,8 +77,7 @@ class _ChangePasswordPageState extends ConsumerState<ChangePasswordPage> {
     } catch (e) {
       if (mounted) {
         setState(() {
-          // 出错时默认已设置密码（注册时必须设置）
+          _isLoadError = true;
-          _hasPassword = true;
           _isLoading = false;
         });
       }
@@ -221,6 +224,23 @@ class _ChangePasswordPageState extends ConsumerState<ChangePasswordPage> {
                           valueColor: AlwaysStoppedAnimation<Color>(Color(0xFFD4AF37)),
                         ),
                       )
+                    : _isLoadError
+                        ? Center(
+                            child: Column(
+                              mainAxisSize: MainAxisSize.min,
+                              children: [
+                                const Icon(Icons.error_outline, color: Colors.red, size: 48),
+                                const SizedBox(height: 12),
+                                const Text('加载失败，请重试', style: TextStyle(color: Colors.red)),
+                                const SizedBox(height: 16),
+                                ElevatedButton(
+                                  onPressed: _loadPasswordStatus,
+                                  style: ElevatedButton.styleFrom(backgroundColor: const Color(0xFFD4AF37)),
+                                  child: const Text('重试', style: TextStyle(color: Colors.white)),
+                                ),
+                              ],
+                            ),
+                          )
                         : SingleChildScrollView(
                         padding: const EdgeInsets.all(16),
                         child: Column(