fix: hide 'Quorum verloren' badge on standalone nodes (#326)

Corporate dashboard's cluster services bar was showing a red "Quorum
verloren" badge for single-node installs. The check used `!== undefined`,
but the API returns `quorate: null` for standalone -- null passes the
undefined check and falls through to falsy, producing the red badge.

Fix: check `standalone === true` first and render a neutral blue
"Standalone" badge (same pattern as datacenter.js). Also switch the
quorate check to `!= null` so actual nulls take the onlineCount fallback.

Author: MrMasterbay