style: 收集箱侧边栏对齐聊天室布局模式，按钮筛选栏区域独立padding，列表贴边

src/web/features/inbox/components/MaterialList.tsx

@@ -110,10 +110,12 @@ export function MaterialList({ loading, materials, onAddClick, onDelete, onSelec
 
   return (
     <div className="app-inbox-sidebar">
-      <Button block icon={<PlusOutlined />} onClick={onAddClick} type="primary">
-        新增素材
-      </Button>
-      <Segmented block onChange={(value) => setFilterStatus(value)} options={segmentedOptions} value={filterStatus} />
+      <div className="app-inbox-sidebar-header">
+        <Button block icon={<PlusOutlined />} onClick={onAddClick} type="primary">
+          新增素材
+        </Button>
+        <Segmented block onChange={(value) => setFilterStatus(value)} options={segmentedOptions} value={filterStatus} />
+      </div>
       <div className="app-inbox-list">
         {loading ? (
           <Skeleton active paragraph={{ rows: 6 }} title={false} />

src/web/styles.css

@@ -259,13 +259,19 @@ body {
   display: flex;
   width: 280px;
   flex-direction: column;
-  gap: var(--ant-margin-sm);
-  padding: var(--ant-padding-sm);
   border-right: 1px solid var(--ant-color-border-secondary);
   border-radius: var(--ant-border-radius-lg);
   background: var(--ant-color-bg-container);
 }
 
+.app-inbox-sidebar-header {
+  display: flex;
+  flex-direction: column;
+  gap: var(--ant-margin-sm);
+  padding: var(--ant-padding-sm);
+  border-bottom: 1px solid var(--ant-color-border-secondary);
+}
+
 .app-inbox-list {
   display: flex;
   flex: 1;