chore: keep internal workflow artifacts local

[MageByte-Zero]

Summary

• Remove completed internal changes/, .superpowers/, and docs/superpowers/ artifacts from the plugin repository.
• Keep public, complete fixtures in docs/examples/, while preserving consumer-owned changes/ workflows.
• Exclude local workflow, contest, and controller-workspace artifacts from both Git and npm packages.
• Make the WorkBuddy default-root assertion independent of the checkout directory name.

Why

The source repository and npm tarball were carrying internal execution material. In particular, npm pack included untracked files, so Git status alone could not protect a local publish.

Validation

• npm run build
• npm test (384 passed, 0 failed)
• npm run validate -- docs/examples/add-dark-mode
• npm run validate -- docs/examples/refactor-auth-boundary
• node scripts/spec-superflow.mjs doctor
• node scripts/spec-superflow.mjs list
• npm pack --dry-run --json package-boundary assertion
• Final independent code review

No version, tag, release, or npm publish is included.