Fix Coolify database networking and health checks

[vezcode]

Summary

• keep the API and PostgREST connected to Coolify’s managed database network without publishing either service
• remove the shell-based PostgREST health check from its distroless image
• start the gateway after PostgREST starts while retaining the API health gate

Production incident verification

• production remained on the previous healthy containers until deployment switchover
• API database DNS and PostgREST health behavior reproduced on the production host
• manual network attachment restored /healthz to HTTP 200
• YAML parsed and git diff --check passed