feat(server): 完成 P2 后端能力（支付幂等、委派回收、OCR异步、审计）

server/prisma/schema.prisma

@@ -171,6 +171,7 @@ model Employee {
 
   submitted_reimbursements ReimbursementForm[] @relation("ReimbursementSubmitter")
   owned_reimbursements     ReimbursementForm[] @relation("ReimbursementOwner")
+  paid_reimbursements      ReimbursementForm[] @relation("ReimbursementPaidBy")
 
   owned_invoices      InvoicePool[] @relation("InvoiceOwner")
   uploaded_invoices   InvoicePool[] @relation("InvoiceUploader")
@@ -276,6 +277,7 @@ model AuditLog {
 
   @@index([request_id])
   @@index([actor_id, created_at])
+  @@index([created_at, actor_id, action], map: "idx_audit_logs_query")
   @@map("audit_logs")
 }
 
@@ -327,15 +329,21 @@ model ReimbursementForm {
   total_amount       Decimal             @default(0) @db.Decimal(14, 2)
   status             ReimbursementStatus @default(draft)
   description        String?
+  payment_voucher_no String?             @db.VarChar(50)
+  payment_date       DateTime?           @db.Date
+  payment_channel    String?             @db.VarChar(20)
+  paid_at            DateTime?
+  paid_by            String?             @db.Uuid
 
   created_at DateTime @default(now())
   created_by String?  @db.Uuid
   updated_at DateTime @updatedAt
   updated_by String?  @db.Uuid
 
-  submitter  Employee   @relation("ReimbursementSubmitter", fields: [submitter_id], references: [id], onDelete: Restrict)
-  owner      Employee   @relation("ReimbursementOwner", fields: [owner_id], references: [id], onDelete: Restrict)
-  department Department @relation(fields: [department_id], references: [id], onDelete: Restrict)
+  submitter        Employee   @relation("ReimbursementSubmitter", fields: [submitter_id], references: [id], onDelete: Restrict)
+  owner            Employee   @relation("ReimbursementOwner", fields: [owner_id], references: [id], onDelete: Restrict)
+  paid_by_employee Employee?  @relation("ReimbursementPaidBy", fields: [paid_by], references: [id], onDelete: SetNull)
+  department       Department @relation(fields: [department_id], references: [id], onDelete: Restrict)
 
   items              ReimbursementItem[]
   invoice_pool_items InvoicePool[]
@@ -345,6 +353,7 @@ model ReimbursementForm {
   @@index([owner_id])
   @@index([submitter_id])
   @@index([department_id])
+  @@index([paid_by])
   @@index([status])
   @@index([reimbursement_date])
   @@map("reimbursement_forms")
@@ -414,6 +423,8 @@ model InvoicePool {
   ocr_attempts     Int         @default(0)
   ocr_last_error   String?
   ocr_completed_at DateTime?
+  ocr_locked_at    DateTime?
+  ocr_lock_owner   String?     @db.VarChar(128)
 
   invoice_code   String?
   invoice_number String?
@@ -447,6 +458,7 @@ model InvoicePool {
   @@index([file_sha256])
   @@index([invoice_code, invoice_number])
   @@index([status])
+  @@index([status, ocr_locked_at, created_at], map: "idx_invoice_pool_ocr_queue")
   @@index([linked_reimbursement_id])
   @@map("invoice_pool")
 }