Health Checks Liveness and Readiness Verification

[Adedayo-Data]

Description

Fixes the HTTP response status code behavior in the GET /health/ready endpoint when critical dependency checks fail.

• Injected NestJS @Res({ passthrough: true }) to dynamically update the HTTP status code.
• Ensures the endpoint correctly responds with 503 Service Unavailable on database failure or when non-critical failures exceed the configured HEALTH_DEGRADED_THRESHOLD.
• Updated unit tests to mock the response object and assert that a 503 status code is set under error conditions.

Verification

• Unit tests run: pnpm --filter backend test health (Passed)
• Application build check: pnpm --filter backend build (Passed)

closes #310

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