Build dispute arbitration with neutral third-party resolver

[Kingsman-99]

Label: complexity: high
Points: 200

Description

There's no mechanism for a payer and creator to escalate a disagreement to a neutral party. This issue adds an optional arbiter address per invoice who can resolve a disputed invoice by forcing release or refund.

Technical Context

Involves types.rs (arbiter: Option<Address> on InvoiceExt), lib.rs — raise_dispute(env, caller, invoice_id) freezes the invoice for arbitration, resolve_dispute(env, arbiter, invoice_id, action: ResolveAction) requires arbiter auth and executes release or refund regardless of normal guards.

Acceptance Criteria

• raise_dispute() callable by creator or any payer; sets a disputed flag, blocks pay()/release()/refund()
• resolve_dispute() requires the configured arbiter's auth; clears disputed
• ResolveAction::Release triggers normal release flow; Refund triggers normal refund flow
• Panics with "no arbiter set" if resolve_dispute called with none configured
• Test: raise dispute blocks pay, arbiter resolves with Refund, payers receive funds back
• All existing cargo tests pass
• cargo clippy passes with zero warnings

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[Abba073]

@Abba073 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi maintainer, i would like to work on this issue

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[kalifabuild-dev]

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Hi maintenance kindly assign me to solve this issue

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[Ebuka321]

@Ebuka321 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Good day. can i work on these issue.

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Congratulations, @Ebuka321! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

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[grantfox-oss]

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

@Ebuka321's PR #240 was approved and merged by @Kingsman-99.

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👏 Great work, @Ebuka321! Keep contributing to Stellar-split.

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This issue has been completed by @Ebuka321 as part of the Stellar Wave Program's 6th Wave 🥳

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