fix: 隐藏验证码输入框光标解决数字显示不全

- 添加 showCursor: false 隐藏光标
- 光标移走后数字不再被遮挡偏移

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/mobile-app/lib/features/auth/presentation/pages/sms_verify_page.dart

@@ -377,6 +377,7 @@ class _SmsVerifyPageState extends ConsumerState<SmsVerifyPage> {
               keyboardType: TextInputType.number,
               textAlign: TextAlign.center,
               maxLength: 1,
+              showCursor: false,  // 隐藏光标，避免光标影响数字显示位置
               inputFormatters: [
                 FilteringTextInputFormatter.digitsOnly,
               ],