Stable v2.8.0

• fix(release): keep demo-scoped commits out of release changelogs
• feat(mail): deliverability dashboard + worker
• feat(packages): per-package PHP defaults for new sites
• fix(nginx): correct + harden the nginx.conf vhost-include ownership
• feat(backup): manually delete a single backup snapshot
• feat(mail): per-domain deliverability score (A–F)
• fix(sites): allow force-delete when the site's server is unreachable
• fix(multiserver): guard node deletion against mail-only subscriptions