Fix PostgreSQL cutover module scope

[azurras]

Summary

• bind deferred PostgreSQL cutover actions to their originating module commands
• preserve private helper resolution after normal Import-Module
• add a regression matching the production dispatcher/import boundary

Production evidence

• the approved cutover stopped before journal creation or writer shutdown with New-ProductionPostgreSqlCutoverPreflight not found
• MongoDB and the website remained running; PostgreSQL status is safe and loopback-only

Verification

• focused cutover suite: 17 passed, 0 failed
• complete Windows operations suite: 768 passed, 28 expected skips, 0 failed
• PowerShell parser: 0 errors
• git diff --check: clean