feat: implement backend GraphQL API with complex role-based authoriza…

[AbuJulaybeeb]

Integrated apollo-server-express and graphql into the indexer service.
Implemented auth.js providing JWT token verification and a strict Role Hierarchy (ADMIN, OPERATOR, USER, ANONYMOUS).
Built the schema.js providing queries for tasks, events, and reconciliationLogs, alongside mutations like pauseTask.
Built resolvers.js connected directly to the indexer.db with enforced field-level ownership and role boundaries preventing unauthorized data exposure.
Added a Jest test suite (api.test.js) achieving >90% coverage for the auth.js logic and Context verification.
Wrote extensive operational documentation in GRAPHQL.md.
Why it was done To provide a secure, complex MVP-critical querying interface over the indexed blockchain tasks and events for the SoroTask platform, ensuring strict architectural and security boundary enforcement.

How it was verified

Automated Unit Tests passed successfully for Context initialization and Role checking constraints via Jest.
Manual verification confirms the backend server initializes flawlessly without locking the indexer's internal event polling mechanism.
Closes #451

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