[Performance] Add database query indexing for analytics

[Xoulomon]

Description:
Add PostgreSQL indexes to the events table to speed up the analytics queries that power the dashboard.

Tasks:

• Add index on (group_id, event_type, created_at) for cycle analytics queries
• Add index on (member_address, event_type) for member history queries
• Measure query execution time before and after with EXPLAIN ANALYZE

Difficulty: medium
Points: 150

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[Mirabliss]

@Mirabliss has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Helllo i would like to work on this issue

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

[drips-wave]

Congratulations, @Mirabliss! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

🧑‍💻 @Mirabliss: 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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🌊 Happy Wave 🌊

[drips-wave]

This issue has been completed by @Mirabliss as part of the Stellar Wave Program's 5th Wave 🥳

😎 @Mirabliss: You earned 200 Points for completing this issue! After the current Wave ends, you'll be eligible for a percentage of the Wave's reward pool based on the percentage of total points you've earned. Learn more here. You can also Leave a review to share your experience working on this issue.

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