Enable npm publish provenance for releases #7

Summary

Enable npm provenance for published
releases of @libredb/libredb, so every published version carries a signed, verifiable attestation
linking the tarball to the exact source commit and the GitHub Actions workflow that built it.

Why

Provenance is a supply-chain integrity signal. With it enabled:

• npm shows a provenance badge on the package page.
• Consumers can run npm audit signatures to cryptographically verify that the published tarball was
  built from this repository, at a specific commit, by our publish.yml workflow — not tampered with
  or published from an unknown machine.

This is consistent with the project's reliability and honesty stance and complements the existing
supply-chain hardening (SHA-pinned actions, least-privilege workflow tokens, the full bun run gate
before publish).

Provenance was intentionally deferred while the repository was private, because it requires a public
repository. That precondition is now met (the repo is public and the package is published from GitHub
Actions), and publish.yml already carries a placeholder note for this work.

Current state

.github/workflows/publish.yml publishes without provenance:

permissions:
  contents: read
# ...
- run: npm publish --access public
  env:
    NODE_AUTH_TOKEN: ${{ secrets.NPMJS_TOKEN }}

0.0.4 (the first release published from the public repo) went out without provenance.

Proposed change

1. Grant the publish job an OIDC token:

permissions:
  contents: read
  id-token: write

2. Add the --provenance flag to the publish step:

- run: npm publish --access public --provenance
  env:
    NODE_AUTH_TOKEN: ${{ secrets.NPMJS_TOKEN }}

(Alternatively, set "provenance": true under publishConfig in package.json; the CLI flag is
preferred here so the behavior is explicit in the workflow.)

Also update the placeholder comment in publish.yml to state that provenance is now enabled.

Preconditions

• Public repository
• Published from GitHub Actions (publish.yml)
• repository field set in package.json (provenance links to it)
• npm CLI >= 9.5 (Node 22 via setup-node ships npm 10+)

Acceptance criteria

• publish.yml adds id-token: write and --provenance.
• The next release (e.g. 0.0.5) publishes successfully with provenance.
• The npm package page shows the provenance badge.
• npm audit signatures reports a valid provenance attestation for the new version.
• The placeholder comment in publish.yml is updated.

Notes

• Provenance applies from the version it is first enabled on; already-published versions (0.0.3,
  0.0.4) will not retroactively gain it.
• No new secret is required. Provenance uses the workflow's OIDC identity; NPMJS_TOKEN still
  authenticates the publish itself.

References

• npm — Generating provenance statements: https://docs.npmjs.com/generating-provenance-statements
• GitHub — Security hardening with OpenID Connect (id-token: write):
  https://docs.github.com/actions/deployment/security-hardening-your-deployments/about-security-hardening-with-openid-connect