fix(release): separate registry environments

[2chevskii]

Summary

Release publications need separate GitHub environments after the npm environment was renamed. Route npm staging through npmjs and GitHub Packages publication through the newly created github-packages environment, with each deployment linking to its registry package page. Run finish_release only when a GitHub release is published, removing the manual trigger and its inputs. Preserve independent matrix jobs, failed-job retries, staged npm publication, and existing PR/edge workflows; update the release guidance.

Validation

• Build, ESLint, Prettier, and documentation build passed for the environment changes.
• After removing the manual trigger, Prettier, actionlint, and git diff --check passed. Only actionlint's outdated ubuntu-26.04 runner-label check was excluded.
• GitHub API confirmed that npmjs and github-packages exist and supplied the GitHub package page URL.
• Release publication was not rerun.