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

Replace Django/Graphene stack with TypeScript Express server using Apollo Server v4
with 4 GraphQL endpoints (public/user/team/m2m) and Prisma ORM mapped to existing tables.

src/schemas/public.ts

@@ -0,0 +1,4 @@
+export const publicTypeDefs = `#graphql
+  type Query { health: String! }
+`
+export const publicResolvers = { Query: { health: () => 'ok' } }