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/schemas/user.ts

@@ -0,0 +1,11 @@
+export const userTypeDefs = `#graphql
+  type Query {
+    health: String!
+  }
+`
+
+export const userResolvers = {
+  Query: {
+    health: () => 'ok',
+  },
+}