Drop fragile STAGING_HOST/PROD_HOST host-detection. The runner's
GITHUB_SERVER_URL reports the internal name (gitea.xenophon), which never
matched the public-DNS vars. Now the API uses GITHUB_SERVER_URL directly
(reliable from CI) and the release-body download links use a single
per-instance PUBLIC_HOST var (gitea.scriptorium / repos.gmgauthier.com).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Replace deprecated `variables.` syntax with `vars.`, add logic to detect
the running environment from GITHUB_SERVER_URL, and update release body
URLs to use the detected HOST instead of a hardcoded domain.
Replace hardcoded gmgauthier/gostations path with ${REPO} variable so release install instructions work correctly regardless of repository owner or name.
