feat: add product to opportunity route, local product sequencing

- Add POST /v1/sales/opportunities/:identifier/products with field-level permission gating
- Add CWForecastItemCreate type for forecast item creation
- Store product display order locally (productSequence Int[] on Opportunity)
- Rewrite resequenceProducts to be local-only (no CW PUT, stable IDs)
- Remove reorderProducts CW util (PUT regenerated IDs & broke procurement)
- Update fetchProducts to apply local ordering with CW sequenceNumber fallback
- Add productSequence to OpportunityController.toJson()
- Update API_ROUTES.md, PERMISSIONS.md, PermissionNodes.ts

prisma/schema.prisma

@@ -185,6 +185,10 @@ model Opportunity {
   companyId String?
   company   Company? @relation(fields: [companyId], references: [id])
 
+  // Local product sequence — array of CW forecast item IDs in display order.
+  // When present, fetchProducts() uses this order instead of CW sequenceNumber.
+  productSequence Int[] @default([])
+
   cwLastUpdated DateTime?
 
   createdAt DateTime @default(now())