feat: add backend REST endpoint POST /settlements

[misrasamuelisiguzor-oss]

Description

Implement the POST /settlements endpoint that proposes a new settlement. The endpoint validates the signer is an authorized settlement signer, confirms the token is on the treasury allowlist, validates the amount, and submits propose_settlement to Soroban RPC.

Requirements and context

• Validate signer is an authorized settlement signer
• Confirm the requested token contract address is on the treasury allowlist
• Validate amount is positive and within acceptable bounds
• Call propose_settlement on the settlement contract via Soroban RPC
• Return settlement ID, initial status, and transaction hash on success
• Follow existing project conventions

Suggested execution

1. Fork the repo and create a branch

   git checkout -b feat/backend-post-settlements
   

2. Implement changes
3. Test and commit

Example commit message

feat: add backend REST endpoint POST /settlements

Guidelines

• Assignment required before starting
• PR description must include: Closes #[issue_id]
• Keep PR description professional and detailed

[ppaker119]

@ppaker119 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi maintainer. I am interested in this issue.

I have experience working across frontend, backend, smart contracts, and developer tooling, and I’m comfortable making targeted fixes and improvements in existing codebases. I’ll ensure the implementation is clean, tested, and aligned with the project requirements.

Thanks!

ℹ️ Repo Maintainers: To accept this application, review their application or assign @ppaker119 to this issue.

[tebney]

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

i would love to work on this issue

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

[Amas-01]

@Amas-01 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello Maintainer
I'll like to work on this Issue. Please Assign me

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Amas-01 to this issue.

[directorfloo]

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

I would love to work on this issue professionally, please assign it to me

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

[drips-wave]

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

🧑‍💻 @tebney: 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

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