Stable v2.8.52

• fix(release): make the TypeScript quality gate actually check types
• chore: untrack docs-site/site build output
• docs: update dev checkout path references to /var/www/enconf-webpanel
• docs(legal): fix dead zkm.netcell-it.com links in terms → zkm.netcell-it.de
• docs: point online-docs help link at docs.enconf.com
• fix(test): make HTTP/2 golden vhost test hermetic
• fix(groupware): enable SOGo Redirect action in per-rule mail Filters
• docs: add "Probleme & Fixes" / "Problems & Fixes" troubleshooting section