chore: include skills directory in npm package

[aliou]

Adds the skills/ directory to the files array in package.json so that the skills are included when the package is published to npm.

Currently, the skills directory exists in the repository but is not included in the published npm package. This change ensures users who install surf-cli via npm will have access to the skills documentation.

Changes:

• Added skills/ to the files array in package.json

Testing:
Can be verified with npm pack --dry-run to confirm skills/ is included in the package.

[aliou]

ffs, sonnet opened this before i could look at it

[aliou]

Anyway for more context: I create nix packages for my deps and more and more I try to vendor the skills with them. When the source of the package is GitHub, it's pretty easy to vendor the skill if it's in the repo.

But! When the package is available in a package registry, I get it the package from there but it requires having the skills available with the package, which is not the case here for surf.

Full session: https://buildwithpi.ai/session/#004dbe4a7f7e9103cba72493c4bd68cc