Add health check for cold storage service

[PeaStew]

Summary

The cold_storage (Shield) service in docker-compose.yml:121-142 has no healthcheck defined, unlike all other services (postgres, mysql, auth_service, hot_storage, docs) which have proper health checks.

Impact

• Docker cannot detect if cold_storage is unhealthy
• Dependent services have no way to wait for cold_storage readiness
• Restart policies may not trigger correctly on silent failures

Affected Files

• docker-compose.yml (lines 121-142)

Recommendation

Add a health check consistent with other services:

healthcheck:
  test: ["CMD", "curl", "-f", "http://localhost:8080/health"]
  interval: 15s
  timeout: 5s
  retries: 10