[Backend] — External Result Feed Client Backoff and Circuit Breaker

[Olowodarey]

Problem
external-result-feed.client.ts hammers the upstream on failure with no backoff or breaker, risking rate-limit bans.

Requirements

• Exponential backoff and a circuit breaker that opens after repeated failures.
• Health signal exposed for monitoring.
• Tests: breaker opens after threshold; half-open probe recovers.

Acceptance Criteria

• The result feed client fails gracefully under upstream outages. Covered by tests.

Files

• backend/src/matches/external-result-feed.client.ts
• backend/src/matches/matches.module.ts
• backend/src/health