Issue 8: Implement GraphQL interface

Description: Expose a GraphQL endpoint at /graphql using Spring GraphQL. This will provide an alternative to REST for flexible, client-driven queries.

Tasks:

•  Add Spring GraphQL dependency to the project
•  Define GraphQL schema files (.graphqls) for:
  • User
  • Project
  • Issue
•  Implement @SchemaMapping or @QueryMapping-based resolvers backed by existing service/repository layers
•  Enable filtering (e.g., status, assignee, project) using GraphQL query arguments
•  Ensure REST and GraphQL coexist without conflict
•  Write example queries for documentation/testing
•  Add unit tests for at least 3 GraphQL resolvers
•  Update Helm chart to expose /graphql endpoint (if applicable)

Estimated Effort: 6 hours

Goal: Support front-end or external clients that prefer a flexible query model, while continuing to support REST for internal usage.