ci(release): fix publish to crates.io and enable changelog generation

[crrow]

Problem

1. release-plz release fails with please provide a non-empty token because CARGO_REGISTRY_TOKEN is not set in .github/workflows/release-plz.yml
2. release-plz.toml has publish = false, preventing crates.io publish
3. No CHANGELOG is generated (blocked by publish being disabled)

Fix

• Change publish = false to publish = true in release-plz.toml and update the comment
• Add CARGO_REGISTRY_TOKEN: ${{ secrets.CARGO_REGISTRY_TOKEN }} to the release job env in .github/workflows/release-plz.yml

Acceptance Criteria

• release-plz.toml has publish = true
• release-plz.yml release job passes CARGO_REGISTRY_TOKEN env var
• CI passes

[crrow]

Already fixed by PR #3.