docs: update skill publishing for committed-skills workflow

[carsonfarmer]

Summary

Update the publishing instructions to reflect the simplified skills management approach.

Changes

Skills are now vendored dependencies that are committed to git:

# Consumers get skills automatically on clone
git clone git@github.com:recallnet/skunkworks-template.git

# Update when ready
gh skill update --all
git add .agents/skills/
git commit -m "chore: update skills"

No bootstrap scripts, no postinstall, no lock files.

See skunkworks-template PR #21.