fix: 通过移除内边距解决验证码数字显示不全问题

- 添加 contentPadding: EdgeInsets.zero 移除默认内边距
- 添加 isDense: true 使用紧凑模式
- 移除之前错误的 showCursor 逻辑

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

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

@@ -232,13 +232,12 @@ class _SmsVerifyPageState extends ConsumerState<SmsVerifyPage> {
   }
 
   void _onCodeChanged(int index, String value) {
-    // 每次输入都触发重建，以更新 showCursor 状态
-    setState(() {
-      // 清除错误信息
-      if (_errorMessage != null) {
+    // 清除错误信息
+    if (_errorMessage != null) {
+      setState(() {
         _errorMessage = null;
-      }
-    });
+      });
+    }
 
     if (value.isNotEmpty) {
       // 输入了字符，移动到下一个
@@ -378,7 +377,6 @@ class _SmsVerifyPageState extends ConsumerState<SmsVerifyPage> {
               keyboardType: TextInputType.number,
               textAlign: TextAlign.center,
               maxLength: 1,
-              showCursor: _controllers[index].text.isEmpty,  // 空时显示光标，有内容时隐藏避免遮挡数字
               inputFormatters: [
                 FilteringTextInputFormatter.digitsOnly,
               ],
@@ -386,6 +384,8 @@ class _SmsVerifyPageState extends ConsumerState<SmsVerifyPage> {
                 counterText: '',
                 filled: true,
                 fillColor: const Color(0xFFF5F5F5),
+                contentPadding: EdgeInsets.zero,  // 移除内边距，让数字完整居中显示
+                isDense: true,
                 border: OutlineInputBorder(
                   borderRadius: BorderRadius.circular(12.r),
                   borderSide: BorderSide.none,