[MEDIUM] Missing Health Check Implementation for Production Readiness

[busybox42]

Problem: Application lacks proper health check endpoints and monitoring for production deployment readiness assessment.

Current State: Missing production health checks:

• No standardized /health endpoint implementation
• Docker Compose uses basic netcat checks instead of application-level health
• Kubernetes health checks are rudimentary
• No dependency health verification (ClamAV, Rspamd, LDAP)
• Missing readiness vs liveness distinction

Production Impact:

• Cannot reliably determine if server is ready to accept connections
• Deployment automation cannot verify successful startup
• Load balancer cannot make intelligent routing decisions
• Difficult to diagnose service degradation

Technical Details:
File locations: /docker-compose.yml:92-96, /k8s/deployment.yaml
Functions affected: Health check endpoints, service monitoring
Dependencies: HTTP server, external service connections

Expected Outcome: Comprehensive health check system with proper HTTP endpoints and dependency verification

Acceptance Criteria:

• Implement /health endpoint with JSON response
• Add /ready endpoint for readiness checks
• Verify external service connectivity (ClamAV, Rspamd, LDAP)
• Update Docker and Kubernetes health checks
• Add metrics exposure for health status
• Document health check API