Implement durable on-chain dispute voting in treasury contract

[Prasiejames]

Closes #410
Closes #411
Closes #412
Closes #413

Summary

Closes the "dispute vote state is volatile" gap described for comebackhere-backend by implementing the durable, on-chain dispute voting that this repo's treasury contract spec (abis/treasury.json, docs/glossary.md) already documents but never implemented.

Context: comebackhere-backend is a sibling repository (built from ../comebackhere-backend per docker-compose.override.yml); disputes.ts is not part of this tree. In this repo, dispute votes had no durable storage at all — vote_dispute_resolution was listed in the ABI and glossary but absent from the contract, and resolve_dispute was an empty stub — so any vote state kept by a backend would live only in memory and be silently lost on process restart or across replicas.

Changes

COMEBACKHERE-contracts/contracts/treasury/src/lib.rs

• New on-chain Dispute record: settlement_id, status (Raised / ResolvedClaimant / ResolvedCounterparty), resolution_weight, voters (dedupes signers), raised_by, reason — stored under DataKey::Dispute(settlement_id) in instance storage.
• raise_dispute: now persists the dispute record, keeps the settlement OnHold, and emits dispute_raised.
• vote_dispute_resolution (new): auth-gated, signer-weight-gated, rejects double votes; accumulates resolution_weight and auto-resolves once cumulative weight ≥ threshold; emits dispute_resolution_voted.
• resolve_dispute: finalizes explicitly once the threshold is met (ThresholdNotMet otherwise).
• New TreasuryError variants: DisputeNotFound, DisputeAlreadyRaised, DisputeNotRaised, AlreadyVoted, UnauthorizedSigner, ThresholdNotMet.
• 8 contract tests covering the full vote lifecycle and failure paths.

COMEBACKHERE-contracts/contracts/treasury/src/events.rs (new) — dispute_raised, dispute_resolution_voted, dispute_resolved events, matching the invoice contract's event conventions.

COMEBACKHERE-contracts/contracts/treasury/Cargo.toml — adds the soroban-sdk testutils dev-dependency for the new tests.

abis/treasury.json — errors block synced to the implemented enum (it previously listed a stale, aspirational set).

docs/glossary.md — documents that dispute votes are stored on-chain and the post-resolution settlement outcome.

Design decisions

• resolve_in_favor mapping: true = in favour of the claimant (dispute raiser) → settlement Cancelled; false = in favour of the counterparty (merchant) → settlement returns to Pending.
• Single-counter resolution: resolution_weight accumulates all votes (per the glossary); the vote that crosses the threshold sets the resolution direction.
• Votes are persisted per-signer in the voters list so a signer can never vote twice and resolution_weight can't be inflated.

Verification

• abis/*.json validated as JSON; the ABI generator's function extraction matches the new source (includes vote_dispute_resolution).
• Docs lint: no new issues introduced by this change (7 pre-existing issues in untouched files remain).
• ⚠️ cargo test was not run: no Rust toolchain is available in the authoring environment. The 8 new tests in the treasury crate should be run (cargo test in COMEBACKHERE-contracts/contracts/treasury/) before merge.

Notes

• Pre-existing (not addressed here): the committed abis/treasury.json remains richer than the generator output (spec fields + aspirational functions like propose_partial_settlement), so make check-abi-snapshots was already failing on main.
• CI's contract job checks out WHEELBACK/COMEBACKHERE-contracts; if this change should also land there, it needs to be mirrored in that repo.

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