[Backend] -- Add Circuit Breaker UI/Monitoring Endpoints for Dependency Failures

[Devsol-01]

Description:
When circuit breakers open, operators need insight. Provide endpoints that expose:

• breaker states per dependency
• recent failure counts
• last error timestamps

Acceptance Criteria:

• Monitoring endpoints added (admin-only).
• Data includes breaker state.
• Documented usage.

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