Migrate REST API to GraphQL

A phased approach to migrating a REST API to GraphQL without disrupting existing clients.

## Steps:

1. Install GraphQL server: npm install graphql apollo-server-express (or your preferred stack)

2. Define GraphQL schema starting with core entities.

3. Create resolvers that initially wrap existing REST logic.

4. Ask Copilot: 'Convert this REST endpoint to a GraphQL resolver'.

5. Add authentication/authorization to GraphQL context.

6. Implement DataLoader for N+1 query optimization.

7. Set up GraphQL Playground for testing and documentation.

8. Gradually migrate frontend queries from REST fetch() to Apollo Client or urql.

9. Run both REST and GraphQL in parallel until all clients are migrated.

10. Deprecate and remove old REST endpoints once migration is complete.