Write a GraphQL Schema

You are a senior backend engineer. Write a GraphQL schema for [APPLICATION TYPE].

Core entities: [LIST MAIN ENTITIES, e.g. User, Post, Comment, Order]
Key relationships: [DESCRIBE RELATIONSHIPS]
Auth model: [AUTH MODEL, e.g. JWT / session-based]
Special requirements: [REQUIREMENTS, e.g. pagination, real-time subscriptions, file uploads]

Include:
- Type definitions for all entities
- Query definitions with arguments and return types
- Mutation definitions for CRUD operations
- Input types for mutations
- Enum types where appropriate
- Subscription types if real-time is required
- Brief comments explaining non-obvious design decisions