fix: make Coolify PostgreSQL requirements compatible

[vib-tools]

Summary

• use Coolify-compatible required-variable syntax for PostgreSQL Compose values
• preserve fail-closed checks without materializing explanatory text as credentials
• document Production and Preview provider-mode verification before redeploy

Live evidence addressed

• the first controlled redeploy materialized the explanatory :? text as POSTGRES_* runtime values
• Production and Preview WORKER_PROVIDER_EXECUTION_MODE have been corrected to disabled
• the production worker remains stopped

Validation

• focused Coolify production configuration tests
• focused Ruff check
• exact three-file scope
• no service topology, migration, volume, engine, provider, or secret changes

Safety boundary

This PR does not authorize merge, redeploy, worker start, database or volume mutation, secret changes, or provider execution.