Add cursor-based pagination to `GET /api/usage` to replace offset/limit on large windows

[greatest0fallt1me]

Description

GET /api/usage uses offset/limit and degrades on developers with millions of events. Add cursor pagination keyed on (created_at, id) so deep paging stays O(log n) on the index.

Requirements and Context

• Extend parsePagination in src/lib/pagination.ts with a cursor branch
• usageEventsRepository.pg.ts adds a keyset query path
• Backwards-compatible with current limit/offset callers
• Must be secure, tested, and documented
• Should be efficient and easy to review

Suggested Execution

1. Fork the repo and create a branch

   git checkout -b feature/usage-cursor-pagination

2. Implement changes
   • src/lib/pagination.ts
   • src/repositories/usageEventsRepository.pg.ts
   • src/routes/usage.ts
3. Test and commit
   • npm test -- usage
   • Cover edge cases (malformed cursor, duplicate timestamps)
   • Include test output and notes in the PR

Example commit message

feat: cursor pagination for /api/usage

Acceptance Criteria

• Cursor encodes created_at+id
• Tampered cursor returns 400
• EXPLAIN shows index keyset
• OpenAPI updated

Guidelines

• Backend (Node/TS): Jest, minimum 90% coverage
• Clear documentation and inline comments
• Timeframe: 96 hours

[helenahelenavanbeek-png]

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

I would like to work on this issue. I have experience with Rust and Soroban smart contract development. I will follow the acceptance criteria and add tests. Excited to contribute. Kindly assign.

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

[grantfox-oss]

🦊 GrantFox — @helenahelenavanbeek-png has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #406)
2. Your PR will be reviewed by the CalloraOrg maintainers

Good luck! Track your progress on GrantFox.

[drips-wave]

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

🧑‍💻 @helenahelenavanbeek-png: 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.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign campaign!

@helenahelenavanbeek-png's PR #570 was approved and merged by @greatest0fallt1me.

🏆 @helenahelenavanbeek-png: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (331 total points). Track your full progress on GrantFox.

👏 Great work, @helenahelenavanbeek-png! Keep contributing to CalloraOrg.

[drips-wave]

This issue has been completed by @helenahelenavanbeek-png as part of the Stellar Wave Program's 6th Wave 🥳

😎 @helenahelenavanbeek-png: 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.

🧑‍💻 Repo maintainers: How'd the contributor do? Leave a review to share your experience working with them.