feat(inbox): 素材持久化 CRUD — 数据库表 + API + 前端接入

- 新增 materials 表（id/projectId/description/associatedDate/status/createdAt/updatedAt）
- 新增 4 个后端 API 路由（list/create/get/delete）+ 13 个测试
- 新增 use-materials hooks（TanStack Query）
- 收集箱页面重构为三层架构（InboxPage + MaterialSidebar + MaterialDetailPanel）
- MaterialCard: Popconfirm 删除确认 + 粗粒度时间格式
- MaterialContent: 展示状态标签 + createdAt
- 更新开发文档 backend.md / frontend.md

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

@@ -0,0 +1,44 @@
+import { Result } from "antd";
+
+import { useDeleteMaterial, useMaterialList } from "../../../shared/hooks/use-materials";
+import { MaterialList } from "./MaterialList";
+
+interface MaterialSidebarProps {
+  onAddClick: () => void;
+  onDelete: (id: string) => void;
+  onSelect: (id: string) => void;
+  projectId: string;
+  selectedId: null | string;
+}
+
+export function MaterialSidebar({ onAddClick, onDelete, onSelect, projectId, selectedId }: MaterialSidebarProps) {
+  const { data, error, isLoading, refetch } = useMaterialList(projectId);
+  const deleteMutation = useDeleteMaterial(projectId);
+
+  const handleDelete = (id: string) => {
+    void deleteMutation.mutate({ materialId: id, projectId }, { onSuccess: () => onDelete(id) });
+  };
+
+  if (error) {
+    return (
+      <div className="app-inbox-sidebar">
+        <Result
+          extra={<button onClick={() => void refetch()}>重试</button>}
+          status="error"
+          subTitle="加载素材列表失败"
+        />
+      </div>
+    );
+  }
+
+  return (
+    <MaterialList
+      loading={isLoading}
+      materials={data?.items ?? []}
+      onAddClick={onAddClick}
+      onDelete={handleDelete}
+      onSelect={onSelect}
+      selectedId={selectedId}
+    />
+  );
+}