Migrate exchange backend from Django to Express + Apollo Server + Prisma

Replace Python/Django/Graphene with TypeScript/Express/Apollo Server.
Same 4 endpoints (public/user/team/m2m), same JWT auth.
Prisma replaces Django ORM for Offer/Request/SupplierProfile.
Temporal and Odoo integrations preserved.

src/db.ts

@@ -0,0 +1,3 @@
+import { PrismaClient } from '@prisma/client'
+
+export const prisma = new PrismaClient()