Indexer: add structured logging with request correlation IDs

[Haroldwonder]

Summary

indexer/src/indexer.ts and graphql.ts log with plain console.log/console.error. There's no structured (JSON) logging and no correlation ID tying a GraphQL request to the downstream database queries it triggers, making production debugging slow.

Acceptance Criteria

• Replace ad-hoc console logging with a structured logger (e.g. pino).
• Each GraphQL request gets a correlation ID propagated through resolver logs.
• Log level configurable via env var, documented in indexer/.env.example.

[iwayemi5]

@iwayemi5 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi, I'd like to work on this issue as I have reviewed the scope I think I should have a PR ready in 50 minutes.

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[Onomebello]

@Onomebello has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello i would like to work on this issue

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[drips-wave]

Congratulations, @Onomebello! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

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