feat(widgets): 优化 LeetCode 卡片样式和功能

- 添加图表图标和用户击败图标
- 优化难度显示，添加颜色区分
- 调整布局和样式，提升可读性
- 添加圆形头像和对勾图标
- 优化错误和空状态显示

lib/widgets/leetcode_card.dart

@@ -135,33 +135,81 @@ class _LeetCodeCardState extends State<LeetCodeCard>
         _progress!['totalQuestionBeatsPercentage'] as double;
 
     return Card(
+      elevation: 3,
+      shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(12)),
+      margin: const EdgeInsets.symmetric(vertical: 8),
       child: Padding(
         padding: const EdgeInsets.all(16.0),
         child: Column(
           crossAxisAlignment: CrossAxisAlignment.start,
           children: [
+            Row(
+              children: [
+                const Icon(Icons.bar_chart, color: Colors.green),
+                const SizedBox(width: 8),
                 const Text(
                   '解题进度',
-              style: TextStyle(fontSize: 18, fontWeight: FontWeight.bold),
+                  style: TextStyle(
+                    fontSize: 18,
+                    fontWeight: FontWeight.bold,
                   ),
-            const SizedBox(height: 8),
+                ),
+              ],
+            ),
+            const SizedBox(height: 12),
             ...acceptedQuestions.map((q) {
               final difficulty = q['difficulty'] as String;
               final count = q['count'] as int;
+              Color difficultyColor = Colors.grey;
+              if (difficulty == 'Easy')
+                difficultyColor = Colors.green;
+              else if (difficulty == 'Medium')
+                difficultyColor = Colors.orange;
+              else if (difficulty == 'Hard') difficultyColor = Colors.red;
+
               return Padding(
-                padding: const EdgeInsets.symmetric(vertical: 4.0),
+                padding: const EdgeInsets.symmetric(vertical: 6.0),
                 child: Row(
                   mainAxisAlignment: MainAxisAlignment.spaceBetween,
-                  children: [Text(difficulty), Text('$count 题')],
+                  children: [
+                    Row(
+                      children: [
+                        Container(
+                          width: 12,
+                          height: 12,
+                          decoration: BoxDecoration(
+                            color: difficultyColor,
+                            shape: BoxShape.circle,
+                          ),
+                        ),
+                        const SizedBox(width: 8),
+                        Text(
+                          difficulty == 'EASY'
+                              ? '简单'
+                              : difficulty == 'MEDIUM'
+                                  ? '中等'
+                                  : '困难',
+                          style: const TextStyle(fontWeight: FontWeight.w500),
+                        ),
+                      ],
+                    ),
+                    Text('$count 题', style: const TextStyle(fontSize: 14)),
+                  ],
                 ),
               );
-            }),
+            }).toList(),
             const Divider(),
             Row(
               mainAxisAlignment: MainAxisAlignment.spaceBetween,
               children: [
-                const Text('击败用户',
+                const Row(
-                    style: TextStyle(fontWeight: FontWeight.bold)),
+                  children: [
+                    Icon(Icons.workspace_premium,
+                        size: 18, color: Colors.green),
+                    SizedBox(width: 6),
+                    Text('击败用户', style: TextStyle(fontWeight: FontWeight.bold)),
+                  ],
+                ),
                 Text('${totalBeatsPercentage.toStringAsFixed(1)}%',
                     style: const TextStyle(
                         fontWeight: FontWeight.bold,
@@ -178,6 +226,9 @@ class _LeetCodeCardState extends State<LeetCodeCard>
   @override
   Widget build(BuildContext context) {
     return Card(
+      shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(16)),
+      elevation: 4,
+      margin: const EdgeInsets.all(16),
       child: Padding(
         padding: const EdgeInsets.all(16.0),
         child: Column(
@@ -188,12 +239,23 @@ class _LeetCodeCardState extends State<LeetCodeCard>
               children: [
                 const Text(
                   'LeetCode 最近提交',
-                  style: TextStyle(fontSize: 20, fontWeight: FontWeight.bold),
+                  style: TextStyle(
+                    fontSize: 20,
+                    fontWeight: FontWeight.bold,
+                    color: Colors.green,
                   ),
-                RotationTransition(
+                ),
+                Container(
+                  decoration: BoxDecoration(
+                    color: Colors.green.shade100,
+                    borderRadius: BorderRadius.circular(20),
+                  ),
+                  padding: const EdgeInsets.all(8),
+                  child: RotationTransition(
                     turns: _refreshController,
                     child: IconButton(
-                    icon: const Icon(Icons.refresh, size: 28),
+                      icon: const Icon(Icons.refresh,
+                          size: 24, color: Colors.green),
                       onPressed: _isLoading
                           ? null
                           : () async {
@@ -202,29 +264,43 @@ class _LeetCodeCardState extends State<LeetCodeCard>
                             },
                     ),
                   ),
+                ),
               ],
             ),
             if (_isLoading)
               Center(
                 child: Padding(
-                  padding: const EdgeInsets.all(16.0),
+                  padding: const EdgeInsets.all(24.0),
                   child: AnimatedBuilder(
                     animation: _refreshController,
                     builder: (_, child) => Transform.rotate(
                       angle: _refreshController.value * 2 * 3.14,
                       child: child,
                     ),
-                    child: const CircularProgressIndicator(),
+                    child: const CircularProgressIndicator(
+                      color: Colors.green,
+                      strokeWidth: 2,
+                    ),
                   ),
                 ),
               )
             else if (_error != null)
               Center(
                 child: Padding(
-                  padding: const EdgeInsets.all(16.0),
+                  padding: const EdgeInsets.all(24.0),
+                  child: Row(
+                    mainAxisAlignment: MainAxisAlignment.center,
+                    children: [
+                      const Icon(Icons.error_outline, color: Colors.red),
+                      const SizedBox(width: 8),
+                      Expanded(
                         child: Text(
                           _error!,
                           style: const TextStyle(color: Colors.red),
+                          textAlign: TextAlign.center,
+                        ),
+                      ),
+                    ],
                   ),
                 ),
               )
@@ -239,8 +315,11 @@ class _LeetCodeCardState extends State<LeetCodeCard>
                         const Center(
                           child: Padding(
                             padding: EdgeInsets.all(16.0),
-                            child:
+                            child: Text(
-                                Text('暂无提交记录', style: TextStyle(fontSize: 16)),
+                              '暂无提交记录',
+                              style:
+                                  TextStyle(fontSize: 16, color: Colors.grey),
+                            ),
                           ),
                         )
                       else
@@ -252,20 +331,40 @@ class _LeetCodeCardState extends State<LeetCodeCard>
                             final submission = _submissions[index];
                             final question = submission['question'];
 
-                            return ListTile(
+                            return Card(
+                              elevation: 2,
+                              shape: RoundedRectangleBorder(
+                                borderRadius: BorderRadius.circular(12),
+                              ),
+                              margin: const EdgeInsets.symmetric(vertical: 6),
+                              child: ListTile(
+                                leading: CircleAvatar(
+                                  backgroundColor: Colors.green,
+                                  radius: 16,
+                                  child: Text(
+                                    question['questionFrontendId'].toString(),
+                                    style: const TextStyle(
+                                      color: Colors.white,
+                                      fontSize: 12,
+                                    ),
+                                  ),
+                                ),
                                 title: Text(
                                   question['translatedTitle'] ??
                                       question['title'],
-                                style: const TextStyle(fontSize: 16),
+                                  style: const TextStyle(
+                                    fontSize: 16,
+                                    fontWeight: FontWeight.bold,
+                                  ),
                                 ),
                                 subtitle: Text(
                                   '提交时间: ${timeago.format(DateTime.fromMillisecondsSinceEpoch(submission['submitTime'] * 1000), locale: 'zh_CN')}',
                                   style: const TextStyle(fontSize: 14),
                                 ),
-                              trailing: Text(
+                                trailing: const Icon(
-                                '#${question['questionFrontendId']}',
+                                  Icons.check_circle,
-                                style: const TextStyle(
+                                  color: Colors.green,
-                                    fontSize: 14, fontWeight: FontWeight.bold),
+                                ),
                               ),
                             );
                           },