Add arbiter assignment to escrow contracts

[mikewheeleer]

Description

EscrowContractData.arbiter is always set to None in create_contract and there is no entrypoint to set it, making dispute resolution impossible. Add a mechanism for the client and freelancer to agree on an arbiter so resolve_dispute has an authorized settler.

Requirements and context

• Scoped to TalentTrust escrow Soroban contract (contracts/escrow).
• Implement assign_arbiter(contract_id, caller, arbiter) requiring caller.require_auth() and that caller is client or freelancer; persist into EscrowContractData.arbiter.
• Reject if an arbiter is already set, if arbiter equals client or freelancer, or if status is past Funded.
• Invariant: arbiter is set at most once and is distinct from both parties; assignment blocked while paused.
• Must be secure, tested, and documented.

Suggested execution

• Fork the repo and create a branch:
  • git checkout -b feature/arbiter-assignment
• Implement changes:
  • contracts/escrow/src/dispute.rs
  • Tests: contracts/escrow/src/test/dispute.rs
  • Docs: docs/escrow/dispute-workflow.md
  • Include rustdoc/NatSpec-style doc comments on public functions
  • Validate security assumptions (auth, overflow, fail-closed state machine, storage TTL, fee accounting)

Test and commit

• Run tests: cargo test
• Cover edge cases (unauthorized callers, double release/refund, expired approvals, fee rounding, paused state)
• Include test output and security notes in the PR

Example commit message

feat(escrow): add arbiter assignment entrypoint

Guidelines

• Minimum 95% test coverage on new/changed code
• Clear documentation
• Timeframe: 96 hours from assignment

[drips-wave]

@mikewheeleer Lacastar2000 could not be assigned to this issue because they have reached the maximum of 4 accepted assignments per organization in the current wave of the Stellar Wave Program.

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[strngecloud]

@strngecloud has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi 👋 am a full-stack developer
I will love to work on this issue please assign

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[whisper011]

@whisper011 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Gm! I'd like to work on this.

I've gone through the issue and understand what needs to be done. I'll keep the fix scoped, clean, and tested — and communicate clearly if anything comes up along the way.

Ready to start immediately. Feel free to assign it!

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[Abd-Standard]

@Abd-Standard has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

please allow me to work on this issue , I am smart contracts developer , I can fix this maintainer

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