fix: update outdated extension names from db-meta-* to metaschema-*

[pyramation]

Summary

Updates outdated PostgreSQL extension names in the pgpm export code:

• db-meta-schema → metaschema-schema
• db-meta-modules → metaschema-modules

These constants are used when generating .control files for exported pgpm modules. The old db-meta-* names no longer exist, causing deployment failures with errors like:

could not open extension control file "/usr/local/share/postgresql/extension/db-meta-schema.control": No such file or directory

Review & Testing Checklist for Human

• Verify extension names are correct - Confirm that metaschema-schema and metaschema-modules are the actual names of the PostgreSQL extensions in your environment
• Test module generation - Run pnpm generate:rls in constructive-db after updating to this version and verify the generated .control files have the correct requires line
• Test deployment - Deploy a generated module to verify the extension dependencies resolve correctly

Recommended test plan:

1. Update constructive-db to use this pgpm version
2. Run pnpm generate:rls
3. Check services/constructive-services/constructive-services.control shows requires = 'plpgsql,metaschema-schema,metaschema-modules'
4. Run integration tests to verify deployment works

Notes

This fix is needed to unblock the RLS baseline generation PR in constructive-db (PR #219), which was failing integration tests due to the outdated extension names.

Link to Devin run: https://app.devin.ai/sessions/23949faa112a4110a435a82d88fb47c1
Requested by: Dan Lynch (@pyramation)

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