Dispute Resolution Management API

[Olowodarey]

When a medical claim is partially approved or denied, stakeholders can open a dispute. We need APIs to manage this dispute lifecycle.

Acceptance Criteria

• Create a DisputeModule and relevant Prisma entities.
• Implement REST endpoints: GET /disputes, POST /disputes, PATCH /disputes/:id.
• Validate that a dispute can only be opened against a verifiable MedicalClaim or transaction.
• Allow adding message logs/evidence to an existing dispute.

---