Dead yamljs dependency removed

The n8n CLI was using yamljs for parsing OpenAPI specifications — a library that has sat untouched for seven years with no maintainers. The yaml package, by contrast, receives regular updates and security patches.

The switch required updating how YAML files are loaded in the public API middleware. The old code imported the default export from yamljs; the new approach imports yaml as a module and reads the file directly before parsing it. This minor API adjustment keeps the functionality intact while using a dependency with active stewardship.

Notably, yamljs will still appear in the dependency tree as a transitive dependency pulled in by curlconverter, but n8n's direct usage has been eliminated. The yaml package version is now centralized in the pnpm workspace catalog, ensuring consistency across all packages.

This change lives in the CLI's public API layer, affecting how OpenAPI documentation is served.