refactor(widgets): 重构卡片组件的样式

- 统一了卡片的阴影、边框和圆角样式
- 调整了卡片的外边距
- 优化了部分卡片的内边距
- 统一了难度等级的命名方式

lib/widgets/gitea_card.dart

@@ -125,6 +125,13 @@ class _GiteaCardState extends State<GiteaCard> {
   @override
   Widget build(BuildContext context) {
     return Card(
+      elevation: 4,
+      shadowColor: Colors.deepPurple.withOpacity(0.3),
+      shape: RoundedRectangleBorder(
+        borderRadius: BorderRadius.circular(16),
+        side: BorderSide(color: Colors.deepPurple.withOpacity(0.1)),
+      ),
+      margin: const EdgeInsets.symmetric(vertical: 8.0),
       child: Padding(
         padding: const EdgeInsets.all(16.0),
         child: Column(

lib/widgets/github_card.dart

@@ -101,6 +101,13 @@ class _GithubCardState extends State<GithubCard> {
   @override
   Widget build(BuildContext context) {
     return Card(
+      elevation: 4,
+      shadowColor: Colors.deepPurple.withOpacity(0.3),
+      shape: RoundedRectangleBorder(
+        borderRadius: BorderRadius.circular(16),
+        side: BorderSide(color: Colors.deepPurple.withOpacity(0.1)),
+      ),
+      margin: const EdgeInsets.symmetric(vertical: 8.0),
       child: Padding(
         padding: const EdgeInsets.all(16.0),
         child: Column(

lib/widgets/kodbox_card.dart

@@ -119,9 +119,13 @@ class _KodBoxCardState extends State<KodBoxCard> {
     final sourceID = isFileOperation ? _getSourceID(desc) : null;
 
     return Card(
-      elevation: 2,
+      elevation: 4,
-      margin: const EdgeInsets.symmetric(vertical: 6.0),
+      shadowColor: Colors.deepPurple.withOpacity(0.3),
-      shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(12)),
+      shape: RoundedRectangleBorder(
+        borderRadius: BorderRadius.circular(16),
+        side: BorderSide(color: Colors.deepPurple.withOpacity(0.1)),
+      ),
+      margin: const EdgeInsets.symmetric(vertical: 5.0),
       child: InkWell(
         onTap: sourceID != null ? () => _launchFileUrl(sourceID) : null,
         splashColor: Colors.deepPurple.withAlpha(30),
@@ -211,9 +215,13 @@ class _KodBoxCardState extends State<KodBoxCard> {
   @override
   Widget build(BuildContext context) {
     return Card(
-      shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(16)),
+      shape: RoundedRectangleBorder(
-      elevation: 4,
+        borderRadius: BorderRadius.circular(20),
-      margin: const EdgeInsets.all(16),
+        side: BorderSide(color: Colors.deepPurple.withOpacity(0.15)),
+      ),
+      elevation: 6,
+      shadowColor: Colors.deepPurple.withOpacity(0.4),
+      margin: const EdgeInsets.symmetric(horizontal: 16, vertical: 8),
       child: Padding(
         padding: const EdgeInsets.all(16.0),
         child: Column(

lib/widgets/leetcode_card.dart

@@ -143,11 +143,11 @@ class _LeetCodeCardState extends State<LeetCodeCard>
         child: Column(
           crossAxisAlignment: CrossAxisAlignment.start,
           children: [
-            Row(
+            const Row(
               children: [
-                const Icon(Icons.bar_chart, color: Colors.green),
+                Icon(Icons.bar_chart, color: Colors.green),
-                const SizedBox(width: 8),
+                SizedBox(width: 8),
-                const Text(
+                Text(
                   '解题进度',
                   style: TextStyle(
                     fontSize: 18,
@@ -161,11 +161,11 @@ class _LeetCodeCardState extends State<LeetCodeCard>
               final difficulty = q['difficulty'] as String;
               final count = q['count'] as int;
               Color difficultyColor = Colors.grey;
-              if (difficulty == 'Easy')
+              if (difficulty == 'EASY')
                 difficultyColor = Colors.green;
-              else if (difficulty == 'Medium')
+              else if (difficulty == 'MEDIUM')
                 difficultyColor = Colors.orange;
-              else if (difficulty == 'Hard') difficultyColor = Colors.red;
+              else if (difficulty == 'HARD') difficultyColor = Colors.red;
 
               return Padding(
                 padding: const EdgeInsets.symmetric(vertical: 6.0),
@@ -226,9 +226,13 @@ 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),
+      shadowColor: Colors.deepPurple.withOpacity(0.3),
+      shape: RoundedRectangleBorder(
+        borderRadius: BorderRadius.circular(16),
+        side: BorderSide(color: Colors.deepPurple.withOpacity(0.1)),
+      ),
+      margin: const EdgeInsets.symmetric(vertical: 8.0),
       child: Padding(
         padding: const EdgeInsets.all(16.0),
         child: Column(
@@ -332,11 +336,11 @@ class _LeetCodeCardState extends State<LeetCodeCard>
                             final question = submission['question'];
 
                             return Card(
-                              elevation: 2,
+                              elevation: 3,
                               shape: RoundedRectangleBorder(
-                                borderRadius: BorderRadius.circular(12),
+                                borderRadius: BorderRadius.circular(16),
                               ),
-                              margin: const EdgeInsets.symmetric(vertical: 6),
+                              margin: const EdgeInsets.symmetric(vertical: 4),
                               child: ListTile(
                                 leading: CircleAvatar(
                                   backgroundColor: Colors.green,