Remove duplicate directories and related infrastructure

Removed duplicate directories from registry/src that now exist in socket-lib:
- constants/
- env/
- external/
- lib/
- packages/
- types/
- utils/

Removed external-related build and validation scripts:
- build-externals.mjs
- fix-external.mjs
- lint-external.mjs
- validate-external.mjs
- check-registry-package-types.mjs

Updated registry/src/index.ts to export only manifest helper and types.

Updated lint and test scripts to remove references to deleted directories:
- test-affected.mjs
- lint.mjs
- lint-affected.mjs

Author: jdalton