[BE-123] Unit tests for the dispute module

[mftee]

Overview

backend/src/dispute/ has 8 files and 2 entities with no tests. Disputes are the project's stated reason for existing, and they encode who may say what about whose land.

Tasks

• Test dispute creation, including that only eligible parties may raise one against a document.
• Test the status lifecycle and rejection of invalid transitions.
• Test access control: a user must not read disputes they are not party to, except for admins.
• Test evidence attachment and its access rules.
• Test resolution recording and that a resolved dispute cannot be silently reopened or edited.
• Target ≥75% coverage.

Acceptance Criteria

• npm run test -- dispute passes at ≥75% coverage.
• A non-party is proven unable to read or modify a dispute.
• Invalid status transitions are rejected.

Notes for Contributors

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