Backend: Add GraphQL API layer alongside REST

[CelestinaBeing]

Summary

The REST API serves campaign data well for simple CRUD, but integrators building complex dashboards (e.g. 'give me all active campaigns with their stats and the last 5 audit log entries in one request') suffer from N+1 request patterns. A GraphQL layer enables efficient data fetching for complex queries.

Problem

• Frontend must make 3+ round trips to get campaign + stats + audit logs
• No subscription mechanism for real-time updates
• Third-party integrators building analytics tools cannot query exactly what they need

Acceptance Criteria

• Add graphql + graphql-yoga (or apollo-server-express) to backend/package.json
• Mount GraphQL at /graphql with GraphiQL explorer (enabled in dev via env flag)
• Schema: Campaign, AuditLog, Stats, Config types with all existing REST fields
• Queries: campaigns(filter, sort, limit, cursor), campaign(id), stats, config
• Mutations: createCampaign, updateCampaign, deleteCampaign (API key auth)
• DataLoader for batched DB queries (prevent N+1)
• Apply the same rate limiter and API key auth middleware as REST
• Add unit tests for resolvers
• Document in backend/openapi.yaml (note: separate schema at /graphql)

References

• backend/src/index.js
• backend/src/dal/

[Opeyemi01-del]

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[presidojay1]

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