Migrated kg-default-nodes to TypeScript

[kevinansfield]

Summary

• migrate packages/kg-default-nodes source, tests, and test helpers from JavaScript to TypeScript
• replace the Rollup/Babel build with tsc-generated ESM/CJS outputs and declaration files
• add TypeScript and flat ESLint configuration for the package
• tighten node factory, parser, and renderer typing across the package
• expose a shared @tryghost/kg-default-nodes/visibility entrypoint and use it from koenig-lexical