[Backend] REST API: Implement Trigger Payout Endpoint

[ONEONUORA]

Description

Implement POST /api/plans/payout to initialize payouts:

• Verifies if the grace period has elapsed.
• Computes final locked amount + yield.
• Iterates over beneficiaries and inserts payout records in PostgreSQL.
• Initiates on-chain and fiat anchor off-ramp distributions.

Acceptance Criteria

• Rejects payout triggers if the grace period is still active.
• Correctly divides the total balance based on allocations.
• Marks the plan as inactive in the database.

[supremeproton02]

@supremeproton02 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi maintainer, can i be assigned to this?

ℹ️ Repo Maintainers: To accept this application, review their application or assign @supremeproton02 to this issue.

[fhayvy]

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

Hi maintainer, please can you assign this issue to me. i'll love to contribute to your project.

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

[grantfox-oss]

🦊 GrantFox — @fhayvy 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 #812)
2. Your PR will be reviewed by the Fracverse maintainers

Good luck! Track your progress on GrantFox.

[drips-wave]

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

🧑‍💻 @fhayvy: 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!

@fhayvy's PR #892 was approved and merged by @ONEONUORA.

🏆 @fhayvy: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (261 total points). Track your full progress on GrantFox.

👏 Great work, @fhayvy! Keep contributing to Fracverse.

[drips-wave]

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

😎 @fhayvy: 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.