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/shared/api.ts

@@ -28,6 +28,11 @@ export interface CreateConversationRequest {
   title?: string;
 }
 
+export interface CreateMaterialRequest {
+  associatedDate: string;
+  description: string;
+}
+
 export interface CreateModelRequest {
   capabilities: ModelCapability[];
   contextLength?: null | number;
@@ -54,6 +59,29 @@ export interface CreateProviderRequest {
 // 前后端共享的类型都放在这个文件中
 // ==========================================
 
+export interface Material {
+  associatedDate: string;
+  createdAt: string;
+  description: string;
+  id: string;
+  projectId: string;
+  status: MaterialStatus;
+  updatedAt: string;
+}
+
+export interface MaterialListResponse {
+  items: Material[];
+  page: number;
+  pageSize: number;
+  total: number;
+}
+
+export interface MaterialResponse {
+  material: Material;
+}
+
+export type MaterialStatus = "approved" | "discarded" | "pending";
+
 export interface Message {
   content: string;
   conversationId: string;