feat(P17B-1,P17B-2): 补齐采购预算闭环与归档模型接口

server/prisma/schema.prisma

@@ -229,9 +229,10 @@ model Employee {
   leave_requests               LeaveRequest[]
   leave_ledgers                LeaveLedger[]
   owned_cost_centers           CostCenter[]        @relation("CostCenterOwner")
-  purchase_requests_applicant  PurchaseRequest[]   @relation("PurchaseRequestApplicant")
-  purchase_requests_submitted  PurchaseRequest[]   @relation("PurchaseRequestSubmitter")
-  purchase_attachments_uploaded PurchaseAttachment[] @relation("PurchaseAttachmentUploader")
+  purchase_requests_applicant   PurchaseRequest[]     @relation("PurchaseRequestApplicant")
+  purchase_requests_submitted   PurchaseRequest[]     @relation("PurchaseRequestSubmitter")
+  purchase_attachments_uploaded PurchaseAttachment[]  @relation("PurchaseAttachmentUploader")
+  purchase_order_archives       PurchaseOrderArchive[] @relation("PurchaseOrderArchiveArchivedBy")
 
   owned_invoices                  InvoicePool[]               @relation("InvoiceOwner")
   uploaded_invoices               InvoicePool[]               @relation("InvoiceUploader")
@@ -584,6 +585,7 @@ model PurchaseRequest {
 
   items              PurchaseRequestItem[]
   attachments        PurchaseAttachment[]
+  order_archive      PurchaseOrderArchive?
   workflow_instances WorkflowInstance[]
 
   @@index([applicant_id, status, updated_at], map: "idx_purchase_requests_applicant_status_updated")
@@ -637,6 +639,23 @@ model PurchaseAttachment {
   @@map("purchase_attachments")
 }
 
+model PurchaseOrderArchive {
+  id                  String   @id @default(uuid()) @db.Uuid
+  purchase_request_id String   @unique @db.Uuid
+  po_no               String
+  contract_no         String?
+  archived_files      Json?
+  archived_at         DateTime @default(now())
+  archived_by         String   @db.Uuid
+
+  purchase_request     PurchaseRequest @relation(fields: [purchase_request_id], references: [id], onDelete: Cascade)
+  archived_by_employee Employee        @relation("PurchaseOrderArchiveArchivedBy", fields: [archived_by], references: [id], onDelete: Restrict)
+
+  @@index([archived_by], map: "idx_purchase_order_archives_archived_by")
+  @@index([archived_at], map: "idx_purchase_order_archives_archived_at")
+  @@map("purchase_order_archives")
+}
+
 model ReimbursementForm {
   id                 String              @id @default(uuid()) @db.Uuid
   form_number        String?             @unique