DAO-governed dispute resolution

[nafiuishaaq]

Description:
Replace single admin dispute resolver with a DAO vote. Requires integration with Soroban DAO contract (or simple token-weighted voting).

Acceptance Criteria:

set_dispute_dao(dao_address: Address) admin function.

resolve_dispute_via_dao(session_id, proposal_id) — submits dispute to DAO.

DAO votes with buyer_share, seller_share as vote options.

After DAO voting period, execute_dao_resolution(session_id) finalizes.

DAO resolution overrides any admin resolution.

Emits DisputeSentToDAO, DisputeResolvedByDAO events.

Fallback to admin if DAO doesn't resolve within 10,000 ledgers.

Labels: dao, governance, decentralization