Add a claim function for unsuccessful bidders in agent_bidding

[devJaja]

Goal: Non-punitive auctions.
Why it matters: Losers currently have cumbersome refund paths.
Proposed scope:

• claim_refund for losers and escrow returns on dispute, with proof of loss, idempotency, and finality marker.
  Acceptance criteria:
• Each loser can claim exactly once.
• No claim after escrow resolution deadline.

[somotochukwu-dev]

@somotochukwu-dev has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi
Please assign this issue to me
Thanks

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

[retkatmun]

@retkatmun has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi Maintainer, I'm a smart contract/full-stack dev (Rust, Soroban, Cairo, TypeScript) focused on secure, clean blockchain code. I've reviewed the issue and can deliver a complete solution within 24 hours. Please assign it to me

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

[prissca]

@prissca has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

i will love to work on this issue

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

[drips-wave]

Congratulations, @prissca! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on August 31, 2026.

🧑‍💻 @prissca: 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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[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox!

@prissca's PR #462 was approved and merged by @devJaja.

🏆 @prissca: You earned 40 FoxPoints for this contribution! Your current tier: Builder (1,862 total points). Track your full progress on GrantFox.

👏 Great work, @prissca! Keep contributing to Epta-Node.