style(dashboard): 调整Dashboard为半透明背景样式

- 左侧区域、右侧区域、底部模块改为半透明背景
- 使用 rgba(45, 65, 131, 0.6) 实现半透明效果
- 保持原有的边框和文字样式

参考计划: .sisyphus/plans/dashboard-center-update.md 布局调整要求

src/views/Dashboard/Index.vue

@@ -557,7 +557,7 @@ onUnmounted(() => {
 .list-card-item {
   width: 25%;
   height: 90%;
-  background: #2d3d5f;
+  background: rgba(45, 65, 131, 0.6);
   border: 1px solid rgba(56, 102, 141, 0.5);
   display: flex;
   padding-left: 15px;
@@ -607,12 +607,12 @@ onUnmounted(() => {
   align-items: center;
   justify-content: center;
   padding: 12px 16px;
-  background: #2d3d5f;
+  background: rgba(45, 65, 131, 0.6);
   border: 1px solid rgba(56, 102, 141, 0.5);
   border-radius: 6px;
   box-shadow: inset 0 0 10px 0 rgba(43, 65, 131, 0.3);
   transition: all 0.3s ease;
-  
+
   &:hover {
     border-color: rgba(56, 102, 141, 0.8);
     box-shadow: inset 0 0 15px 0 rgba(43, 65, 131, 0.5);