feat: add arbitration council escalation for split disputes

[0yOla]

Overview

This PR adds an escalation path for disputes that community vote cannot resolve. When a market's community vote fails to reach the required quorum threshold, the dispute can now be escalated to a trusted arbitration council instead of being decided by a split community vote.

Related Issue

Changes

⚖️ Dispute Escalation

• [MODIFY] contracts/disputes/src/lib.rs
  • Added quorum threshold check on community vote resolution so disputes with votes below the required threshold are flagged as unresolved rather than finalized.
  • Added an escalation path that routes unresolved/split disputes to a trusted arbitration council for final resolution.
  • Added council resolution handling so escalated disputes can be settled by the arbitration council and recorded on the dispute.

Verification Results

cargo test -p disputes
✅ dispute resolution and escalation tests passed

Acceptance Criteria	Status
Disputes below quorum threshold are not resolved by community vote alone	✅ Quorum check gates community resolution
Split disputes have an escalation path to a trusted arbitration council	✅ Escalation routes unresolved disputes to the council
Council can resolve escalated disputes	✅ Council resolution recorded on the dispute

Closes #26

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