Risk score calculation job

[Martins0152]

Description
Implement POST /:id/risk-score, which calculates and persists a beneficiary's riskScore (0-100) using a defined, documented heuristic (not a black box).

Acceptance Criteria

• The scoring logic is implemented as a pure, unit-testable function in src/services/ - not inline in the controller.
• Document the exact factors used (e.g. KYC status, campaign assignment count, distribution history anomalies) in a code comment and in /docs.
• Endpoint is restricted to ADMIN/ORGANIZATION.
• Score is clamped to 0-100 and persisted on the Beneficiary record.
• Unit tests cover at least 3 distinct input scenarios producing different scores.
• Documented in openapi.yaml.

Suggested reward: $30-$40