feat: implement /api/logs reverse proxy with per-endpoint circuit bre…

[TechBroAfrica]

closes #944

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Title: feat: add per-endpoint circuit breaker for downstream calls on /api/logs

Description:
This PR introduces a dedicated proxy router for downstream logging services with per-endpoint circuit breaking, successfully fulfilling the requirements for the GrantFox FWC26 campaign.

The /api/logs endpoint acts as a resilient proxy that fast-fails with an HTTP 503 Service Unavailable if the downstream service experiences an outage.

🚀 Key Changes

• src/routes/logs.ts: Added a new reverse proxy router matching ALL /api/logs/:endpoint(*)?. It tracks downstream failures dynamically per-endpoint using the BreakerRegistry.
• src/lib/circuitBreaker.ts: Added an optional onOpenError callback to the CircuitBreakerConfig. This safely enables the logs route to fast-fail with a customizable ServiceUnavailableError (503) without mutating the global 502 Bad Gateway behaviors currently expected for Horizon endpoints.
• src/index.ts: Registered the new logsRouter centrally.
• src/routes/logs.test.ts: Implemented a comprehensive test suite that verifies the circuit breaker correctly triggers the 503 Service Unavailable response after reaching the failure threshold (5 attempts).
• docs/api-logs.md: Created new documentation explicitly covering the expected API interface, parameters, and its fast-fail circuit breaker behavior.

✅ Testing & Validation

• Full unit tests implemented (npm test -- src/routes/logs.test.ts).
• Code style strictly adheres to the repo's lint configuration (no unused variables).
• No any type violations introduced.
• Tested the fast-fail 503 behavior natively against mock setups.

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[TechBroAfrica]

@greatest0fallt1me kindly review, conflict resolve.

[greatest0fallt1me]

CI green, LGTM ✨ merged.