feat(health): define machine-readable health status enums and OpenAPI contract

[syntaxsuuvam-spec]

Summary

Defines machine-readable ComponentStatus and HealthStatus TypeScript enums in HealthResponseDto, decorates them with @ApiProperty OpenAPI enum metadata, and synchronizes the probe contract documentation in docs/kubernetes-health-probes.md.

Closes #288

Changes

• src/health/dto/health-response.dto.ts: Exported ComponentStatus (UP, DOWN, DEGRADED, UNKNOWN) and HealthStatus (OK, DEGRADED, ERROR) enums with OpenAPI @ApiProperty({ enum, enumName }) annotations.
• docs/kubernetes-health-probes.md: Added enum definitions, meanings, and HTTP status mappings for probes.

Verification

• Fully backwards-compatible with existing controller and service union types.
• Zero impact on liveness probe execution path.
• Verified TypeScript compatibility.