Replay/duplicate protection via `eventId`

[codebestia]

Track recently-seen eventIds per device (Redis set with TTL) and drop replays. Combined with client-generated messageId idempotency, this prevents duplicate persistence and delivery when clients retry on flaky networks.

Acceptance criteria:

• Re-sent eventId within the window is ignored
• Legitimate distinct events always processed
• Window TTL configurable

[aigbagbobila]

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

Hi Maintainer Can I resolve this kindly assign

ℹ️ Repo Maintainers: To accept this application, review their application or assign @aigbagbobila to this issue.

[drips-wave]

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

🧑‍💻 @aigbagbobila: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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